[Question] Regarding the new _OSC capability to negotiate type of CPU Hotplug support (i.e. present/enable)
Hi James, Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
[1] https://gitlab.arm.com/linux-arm/linux-jm/-/commit/220b0d8b0261d7467c8705e6f...
Thanks Salil
Hi Salil,
On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
I'm aware that the ACPI side of the cpu 'driver' is visible in sysfs when it shouldn't be, I plan to fix that once I have something I can test it with.
Thanks,
James
Hi James,
From: James Morse james.morse@arm.com Sent: Tuesday, June 6, 2023 11:32 AM
Hi Salil,
On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Ok. When do you plan to send the 'RFC vN' with this _OSC change?
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
Do we always need to support any form of hotplug in kernel? Can we have below:
1. Physical Hotplug Support 2. Virtual Hotplug Support 3. No Hotplug Support at all i.e. defaults to earlier kernel behavior without using any other information except capabilities from firmware/VMM
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
I do understand and we have an agreement on this. We are not manipulating _STA.PRES bit.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
Ok.
Why not use the 'osc_sb_hotplug_enabled_support_confirmed' flag to totally disable ANY kind of cpu hotplug at init time?
I'm aware that the ACPI side of the cpu 'driver' is visible in sysfs when it shouldn't be, I plan to fix that once I have something I can test it with.
Ok. I will share the Qemu port today if you are waiting for that.
Thanks Salil
Hi Salil,
On 06/06/2023 15:49, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Tuesday, June 6, 2023 11:32 AM On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Ok. When do you plan to send the 'RFC vN' with this _OSC change?
Once I can test it! How are the qemu changes going?
There is no point posting it without testing the changes Oliver proposed. I've done bits of that with the kvmtool version I shared, but no-one can test this thing end to end until the Qemu side of it is updateed to match.
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
Do we always need to support any form of hotplug in kernel? Can we have below:
- Physical Hotplug Support
- Virtual Hotplug Support
The kernel can't tell these two apart. What we actually have is: 1. Dynamically making a CPU present/not-present 2. Dynamically making a CPU enabled/not-enabled
I see no reason not to enable (2) for all architectures, unless it turns out x86 has platforms which randomly change that bit assuming its ignored.
- No Hotplug Support at all i.e. defaults to earlier kernel behavior without using any other information except capabilities from firmware/VMM
I'm not sure what your question is here. Why would you want to disable OS support for toggling the enabled bit? Blocking eject-requests is the only reason I can think of ... but there is no-way to do that today... why do we need one?
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
I do understand and we have an agreement on this. We are not manipulating _STA.PRES bit.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
Ok.
Why not use the 'osc_sb_hotplug_enabled_support_confirmed' flag to totally disable ANY kind of cpu hotplug at init time?
Because that would be extra work and extra code. Why is it needed?
I think I'm missing the use-case for linux not supporting this when the firmware does.
I'm aware that the ACPI side of the cpu 'driver' is visible in sysfs when it shouldn't be, I plan to fix that once I have something I can test it with.
Ok. I will share the Qemu port today if you are waiting for that.
Great thanks. I haven't the time to look at this until at least the week after next.
Thanks,
James
Hi James,
From: James Morse james.morse@arm.com Sent: Wednesday, June 7, 2023 11:00 AM
Hi Salil,
On 06/06/2023 15:49, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Tuesday, June 6, 2023 11:32 AM On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Ok. When do you plan to send the 'RFC vN' with this _OSC change?
Once I can test it! How are the qemu changes going?
There is no point posting it without testing the changes Oliver proposed. I've done bits of that with the kvmtool version I shared, but no-one can test this thing end to end until the Qemu side of it is updateed to match.
Sure, but to be able to test Qemu patches one need your rebased version of the kernel. It is up to you whether you want to make it public or not. I did wait for that and then proceeded to create my own version of your 24th Feb 2023 Kernel changes.
Qemu Repo of the latest port (with Oliver's Uptons Patches): Link: https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v1-port11052023.dev-1
Maybe, you can share a quick port of your kernel changes on gitlab so that people can get untied although I can share my own version of the port as well?
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
Do we always need to support any form of hotplug in kernel? Can we have below:
- Physical Hotplug Support
- Virtual Hotplug Support
The kernel can't tell these two apart. What we actually have is:
- Dynamically making a CPU present/not-present
- Dynamically making a CPU enabled/not-enabled
I see no reason not to enable (2) for all architectures, unless it turns out x86 has platforms which randomly change that bit assuming its ignored.
Agreed. So the check for both capabilities is a requirement. Could we have a case where Hotplug is not supported at all? Should we put a print in the kernel checking nothing else but these capabilities to detect any such random event in case hotplug is not supported at all?
- No Hotplug Support at all i.e. defaults to earlier kernel behavior without using any other information except capabilities from firmware/VMM
I'm not sure what your question is here. Why would you want to disable OS support for toggling the enabled bit? Blocking eject-requests is the only reason I can think of ... but there is no-way to do that today... why do we need one?
Sorry, I just meant to disable Hotplug support by detecting these _OSC capability Bits.
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
I do understand and we have an agreement on this. We are not manipulating _STA.PRES bit.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
Ok.
Why not use the 'osc_sb_hotplug_enabled_support_confirmed' flag to totally disable ANY kind of cpu hotplug at init time?
Because that would be extra work and extra code. Why is it needed?
I think I'm missing the use-case for linux not supporting this when the firmware does.
Just to make aware guest user about any such spurious hotplugging event when VMM/firmware does not supports it. Just a knob to enable/disable the hotplug behavior without relying on the ACPI _STA.{PRES, ENA} Bits?
I'm aware that the ACPI side of the cpu 'driver' is visible in sysfs when it shouldn't be, I plan to fix that once I have something I can test it with.
Ok. I will share the Qemu port today if you are waiting for that.
Great thanks. I haven't the time to look at this until at least the week after next.
Shared the link (see above)
Thanks Salil
Hi Salil,
On 07/06/2023 12:29, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Wednesday, June 7, 2023 11:00 AM On 06/06/2023 15:49, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Tuesday, June 6, 2023 11:32 AM On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Ok. When do you plan to send the 'RFC vN' with this _OSC change?
Once I can test it! How are the qemu changes going?
There is no point posting it without testing the changes Oliver proposed. I've done bits of that with the kvmtool version I shared, but no-one can test this thing end to end until the Qemu side of it is updateed to match.
Sure, but to be able to test Qemu patches one need your rebased version of the kernel. It is up to you whether you want to make it public or not. I did wait for that and then proceeded to create my own version of your 24th Feb 2023 Kernel changes.
This:? https://op-lists.linaro.org/archives/list/linaro-open-discussions@op-lists.l...
Yes - that was to allow the Qemu changes to be tested. I'm aware of the chicken/egg problem.
I didn't keep rebasing it as it didn't look like any progress was being made.
Qemu Repo of the latest port (with Oliver's Uptons Patches): Link: https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v1-port11052023.dev-1
Thanks for this,
Maybe, you can share a quick port of your kernel changes on gitlab so that people can get untied although I can share my own version of the port as well?
There is no point doing it quickly if its not done correctly. I'll try and post an RFC before kvm-forum but I can't promise anything.
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
Do we always need to support any form of hotplug in kernel? Can we have below:
- Physical Hotplug Support
- Virtual Hotplug Support
The kernel can't tell these two apart. What we actually have is:
- Dynamically making a CPU present/not-present
- Dynamically making a CPU enabled/not-enabled
I see no reason not to enable (2) for all architectures, unless it turns out x86 has platforms which randomly change that bit assuming its ignored.
Agreed. So the check for both capabilities is a requirement.
Not sure where that came from. The OS should advertise which of these its supports. On arm64, firmware can rely on both being advertised, as neither are supported today. On x86, firmware can only rely on the enabled version, as existing kernels support toggling present, but don't use the _OSC.
Could we have a case where Hotplug is not supported at all?
Yes, that is what arm64 has today.
Should we put a print in the kernel checking nothing else but these capabilities to detect any such random event in case hotplug is not supported at all?
The series adds something like that for the present case: https://gitlab.arm.com/linux-arm/linux-jm/-/commit/8e3e891c8fff7260f14a2c21a...
I still don't see a reason to disable the 'enabled' version.
- No Hotplug Support at all i.e. defaults to earlier kernel behavior without using any other information except capabilities from firmware/VMM
I'm not sure what your question is here. Why would you want to disable OS support for toggling the enabled bit? Blocking eject-requests is the only reason I can think of ... but there is no-way to do that today... why do we need one?
Sorry, I just meant to disable Hotplug support by detecting these _OSC capability Bits.
In firmware, sure - that is what the _OSC bits are for. In the OS ... that would be extra work, and for what reason? If the OS doesn't support it, the device-check/eject-request stuff will never be triggered.
The _OSC is for firmware's benefit, I don't see a need to try and double-check that the firmware implemented it correctly.
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
I do understand and we have an agreement on this. We are not manipulating _STA.PRES bit.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
Ok.
Why not use the 'osc_sb_hotplug_enabled_support_confirmed' flag to totally disable ANY kind of cpu hotplug at init time?
Because that would be extra work and extra code. Why is it needed?
I think I'm missing the use-case for linux not supporting this when the firmware does.
Just to make aware guest user about any such spurious hotplugging event when VMM/firmware does not supports it.
This sounds like validating firmware from the OS. I'd prefer not to add extra code doing this.
Just a knob to enable/disable the hotplug behavior without relying on the ACPI _STA.{PRES, ENA} Bits?
For what reason? Why would someone want to do this? Without a reason is pointless configurability that has to be tested.
The only reason I can fathom is "I don't trust my firmware - ignore its attempts to offline CPUs" ... but firmware can prevent them coming online in the first place, and eject-request is the one thing that does work on arm64 today (by accident). I think we can kick this down the road until someone has a strong reason for needing it.
Thanks,
James
Hi James,
From: James Morse james.morse@arm.com Sent: Thursday, June 8, 2023 5:47 PM Hi Salil,
On 07/06/2023 12:29, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Wednesday, June 7, 2023 11:00 AM On 06/06/2023 15:49, Salil Mehta wrote:
From: James Morse james.morse@arm.com Sent: Tuesday, June 6, 2023 11:32 AM On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Ok. When do you plan to send the 'RFC vN' with this _OSC change?
Once I can test it! How are the qemu changes going?
There is no point posting it without testing the changes Oliver proposed. I've done bits of that with the kvmtool version I shared, but no-one can test this thing end to end until the Qemu side of it is updateed to match.
Sure, but to be able to test Qemu patches one need your rebased version of the kernel. It is up to you whether you want to make it public or not. I did wait for that and then proceeded to create my own version of your 24th Feb 2023 Kernel changes.
This:? https://op-lists.linaro.org/archives/list/linaro-open-discussions@op-lists.l...
Yes - that was to allow the Qemu changes to be tested. I'm aware of the chicken/egg problem.
I didn't keep rebasing it as it didn't look like any progress was being made.
Ok, yes. I was in mid of testing/fixing various other bugs you and others had reported at that time and testing the migration part as agreed on the 3th Feb 2023 LOD call.
But earlier in March I got pulled into some higher priority project with immediate deadline (prioritized by management internally) so had to focus totally on that during March and April and only picked-up in May when I realized Oliver's patches had already become part of the mainline at the start of April.
Plus, the branch mentioned within the messages in above link you shared
https://gitlab.arm.com/linux-arm/linux-jm/-/tree/virtual_cpu_hotplug/snapsho...
was missing some fixes reported by Miguel to me through a different channel. These fixes were present in your similar but other RFC branch of 24th Feb 2024 (below link).
https://gitlab.arm.com/linux-arm/linux-jm/-/tree/virtual_cpu_hotplug/rfc/sna...
Hence, I had to create a new kernel version in any case to test all the reported fixes as no single kernel branch had all the fixes in it.
But yes, I agree it is a chicken-egg problem, Anyways it’s a history now and we do have latest working Qemu and kernel branches here. Vishnu and Miguel have lightly tested it and basic working seems to be okay and further testing is in progress.
Qemu Repo of the latest port (with Oliver's Uptons Patches): Link: https://github.com/salil-mehta/qemu.git virt-cpuhp-armv8/rfc-v1-port11052023.dev-1
Thanks for this,
Maybe, you can share a quick port of your kernel changes on gitlab so that people can get untied although I can share my own version of the port as well?
There is no point doing it quickly if its not done correctly. I'll try and post an RFC before kvm-forum but I can't promise anything.
Agreed. You can take your time. No rush. Testing is being done using the kernel branch I had shared. Please share your branch once you are convinced and done your part of testing. Your branch can be used later for final testing.
Q2: Have you intentionally omitted below function in the _OSC related kernel change shared in the repository [1]? bool acpi_processor_hotplug_enabled_supported(void)
Is this a build error? Or do you mean the lack of symmetry between handshaking support for the present and enabled bits?
There is no reason to forbid the enable/disabled support if firmware didn't do the handshake. The handshake is there for firmwares benefit, not the OS.
Do we always need to support any form of hotplug in kernel? Can we have below:
- Physical Hotplug Support
- Virtual Hotplug Support
The kernel can't tell these two apart. What we actually have is:
- Dynamically making a CPU present/not-present
- Dynamically making a CPU enabled/not-enabled
I see no reason not to enable (2) for all architectures, unless it turns out x86 has platforms which randomly change that bit assuming its ignored.
Agreed. So the check for both capabilities is a requirement.
Not sure where that came from. The OS should advertise which of these its supports. On arm64, firmware can rely on both being advertised, as neither are supported today. On x86, firmware can only rely on the enabled version, as existing kernels support toggling present, but don't use the _OSC.
Ah, yes, I missed the last point.
Could we have a case where Hotplug is not supported at all?
Yes, that is what arm64 has today.
Should we put a print in the kernel checking nothing else but these capabilities to detect any such random event in case hotplug is not supported at all?
The series adds something like that for the present case: https://gitlab.arm.com/linux-arm/linux-jm/-/commit/8e3e891c8fff7260f14a2c21a...
I still don't see a reason to disable the 'enabled' version.
- No Hotplug Support at all i.e. defaults to earlier kernel behavior without using any other information except capabilities from firmware/VMM
I'm not sure what your question is here. Why would you want to disable OS support for toggling the enabled bit? Blocking eject-requests is the only reason I can think of ... but there is no-way to do that today... why do we need one?
Sorry, I just meant to disable Hotplug support by detecting these _OSC capability Bits.
In firmware, sure - that is what the _OSC bits are for. In the OS ... that would be extra work, and for what reason? If the OS doesn't support it, the device-check/eject-request stuff will never be triggered.
The _OSC is for firmware's benefit, I don't see a need to try and double- check that the firmware implemented it correctly.
In contrast toggling the present bit is forbidden if the OS said it didn't support it, as the architecture code expects the machine to catch fire if you do this.
I do understand and we have an agreement on this. We are not manipulating _STA.PRES bit.
Q3: I am sure you would want to extend usage of these APIs in the acpi_processor.c as well to decide what kind of hotplug (if any) is enabled? Is code related to _OSC changes complete?
This is a leading question, but I can't tell what it is...
I haven't been able to test that _OSC code beyond what I can hack up with the FVP, so there are probably bits missing. Did you have something specific in mind?
Ok.
Why not use the 'osc_sb_hotplug_enabled_support_confirmed' flag to totally disable ANY kind of cpu hotplug at init time?
Because that would be extra work and extra code. Why is it needed?
I think I'm missing the use-case for linux not supporting this when the firmware does.
Just to make aware guest user about any such spurious hotplugging event when VMM/firmware does not supports it.
This sounds like validating firmware from the OS. I'd prefer not to add extra code doing this.
Just a knob to enable/disable the hotplug behavior without relying on the ACPI _STA.{PRES, ENA} Bits?
For what reason? Why would someone want to do this? Without a reason is pointless configurability that has to be tested.
The only reason I can fathom is "I don't trust my firmware - ignore its attempts to offline CPUs" ... but firmware can prevent them coming online in the first place, and eject-request is the one thing that does work on arm64 today (by accident). I think we can kick this down the road until someone has a strong reason for needing it.
Ok. Let us defer this discussion.
Thanks Salil.
Hi Salil
On 6/9/23 15:34, Salil Mehta wrote:
From: James Morse james.morse@arm.com
Just a knob to enable/disable the hotplug behavior without relying on the ACPI _STA.{PRES, ENA} Bits?
For what reason? Why would someone want to do this? Without a reason is pointless configurability that has to be tested.
The only reason I can fathom is "I don't trust my firmware - ignore its attempts to offline CPUs" ... but firmware can prevent them coming online in the first place, and eject-request is the one thing that does work on arm64 today (by accident). I think we can kick this down the road until someone has a strong reason for needing it.
Ok. Let us defer this discussion.
Maybe someone at KVM forum has a need for this - were you able to travel today? If so, what time will you be at the venue tomorrow to swap notes and produce a combined presentation. The slides I have are attached.
If not, were you able to pre-record a video ... or should I dramatically expand the material I have?!
In terms of testing, I've pinned down another problem now that _STA reports 'functional' from boot, but I've not published the branch yet.
Thanks,
James
Hi James, Thanks for reaching out.
From: James Morse james.morse@arm.com Sent: Tuesday, June 13, 2023 4:29 PM
Hi Salil
On 6/9/23 15:34, Salil Mehta wrote:
From: James Morse james.morse@arm.com
Just a knob to enable/disable the hotplug behavior without relying on the ACPI _STA.{PRES, ENA} Bits?
For what reason? Why would someone want to do this? Without a reason is pointless configurability that has to be tested.
The only reason I can fathom is "I don't trust my firmware - ignore its
attempts to
offline CPUs" ... but firmware can prevent them coming online in the
first place, and
eject-request is the one thing that does work on arm64 today (by
accident).
I think we can kick this down the road until someone has a strong reason for needing it.
Ok. Let us defer this discussion.
Maybe someone at KVM forum has a need for this - were you able to travel today?
Yes, finally with national carrier. They could not overlook NHS's final word :) I am at Prague now...waiting for train.. Will reach Brno 11'sh tonight.
If so, what time will you be at the venue tomorrow to swap notes and produce a combined presentation. The slides I have are attached.
Yes, good idea. But still not completely done yet with my presentation. Need to refine to be able to present quickly. Will definitely have to skip some slides details while speaking. (thanks to Jonathan for his very valuable time today and some very good points to consider)
Can come over there early so that we can first discuss the plan and then I can continue refining & completing the left overs.
If you have already reached and seen the venue then let me know the place and time where we can catch for the sync-up tomorrow.
If not, were you able to pre-record a video ... or should I dramatically expand the material I have?!
I will bring slides tomorrow. Roughly 15 of them...still points left to cover...need to think a way to present them quickly.
In terms of testing, I've pinned down another problem now that _STA reports 'functional' from boot, but I've not published the branch yet.
Sure, let us discuss all of that at the venue. Good to jot down all these.
Thanks Salil
Hi guys,
(CC: +Jonathan, you asked about this on the call)
On 6/6/23 11:31, James Morse via Linaro-open-discussions wrote:
On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Done! Its visible to me here:
https://bugzilla.tianocore.org/show_bug.cgi?id=4481
Thanks,
James
On Wed, 14 Jun 2023 10:58:15 +0100 James Morse james.morse@arm.com wrote:
Hi guys,
(CC: +Jonathan, you asked about this on the call)
On 6/6/23 11:31, James Morse via Linaro-open-discussions wrote:
On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Done! Its visible to me here:
From a quick look, LGTM.
Naturally I've forgotten my mantis password since I last looked at one of these so can't see that bit yet... I assume it's the usual reference to the public version being the right place to discuss anyway.
Jonathan
Thanks,
James
Hi Salil,
I've pushed the branch here: https://gitlab.arm.com/linux-arm/linux-jm/-/commits/virtual_cpu_hotplug/rfc/...
I've not tested the qemu TCG workarounds .. but I figure I'm the only one that cares about those! I've not done any testing on x86 for this - I plan to do that before posting.
Thanks,
James
Hi James,
From: James Morse james.morse@arm.com Sent: Wednesday, June 14, 2023 5:04 PM
Hi Salil,
I've pushed the branch here:
https://gitlab.arm.com/linux-arm/linux-jm/-/commits/virtual_cpu_hotplug/rfc/...
I had updated the slides yesterday to include this branch. I presume you Have done the preliminary testing with the branch I share din LOD meeting.
I've not tested the qemu TCG workarounds .. but I figure I'm the only one that cares about those!
Sure, I have not done testing for that either and the code been for long. For quick prototyping I have used TCG earlier but eventually had to switch to test the accel mode. Since then I have not been maintaining TCG part. will check some time if it still works :)
There was fix from Miguel for crash during multiple plug problem I reported in my first RFC.
I've not done any testing on x86 for this - I plan to do that before posting.
No issues. Take your time.
Thanks for the great presentation yesterday! Salil.
Hi guys,
(CC: +Russell)
On 14/06/2023 14:01, Jonathan Cameron wrote:
On Wed, 14 Jun 2023 10:58:15 +0100 James Morse james.morse@arm.com wrote:
On 6/6/23 11:31, James Morse via Linaro-open-discussions wrote:
On 05/06/2023 11:26, Salil Mehta wrote:
Few questions related to new _OSC capabilities to negotiate the type of CPU hotplug(if any):
Q1: ACPI Standard Update: Do we have any Bugzilla-id for the change related to these new _OSC capabilities for the type of CPU hotplug support (i.e. Enabled/Present cpu)?
I don't think so. I was intending on this being code-first, as and when this is on the mailing list I'd poke the arm people that look after the ACPI stuff to do ... what ever is necessary.
Done! Its visible to me here:
From a quick look, LGTM.
Naturally I've forgotten my mantis password since I last looked at one of these so can't see that bit yet... I assume it's the usual reference to the public version being the right place to discuss anyway.
It sounds like this is getting bogged down - it might help to re-iterate the use-case?
Could the folk who would benefit from the VMM knowing that the guest supports some form of hotplug comment on the above bugzilla ticket to describe what that is used for.
Thanks,
James
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Salil Mehta