Hello,
From: James Morse [mailto:james.morse@arm.com] Sent: Friday, October 21, 2022 10:46 AM To: Russell King (Oracle) linux@armlinux.org.uk; Salil Mehta salil.mehta@huawei.com Cc: Joyce Qi joyce.qi@linaro.org; Jonathan Cameron jonathan.cameron@huawei.com; Lorenzo Pieralisi lorenzo.pieralisi@linaro.org; Jean-Philippe Brucker jean-philippe@linaro.org; Jean-Philippe Brucker jean-philippe.brucker@arm.com; linaro-open-discussions@op-lists.linaro.org; salil.mehta@opnsrc.net; mehta.salil.lnk@gmail.com Subject: Re: Linaro-open-discussions Digest, Vol 25, Issue 3
Hi Russell, Salil,
On 21/10/2022 08:38, Russell King (Oracle) wrote:
On Fri, Oct 21, 2022 at 12:28:23AM +0000, Salil Mehta wrote:
Hi James, It totally skipped my mind earlier to mention that apart from what I have
already
shared through the below repositories, and as discussed in early September
on LOD,
I have also been experimenting with another approach (nothing new but something similar and based on yours and JPBs suggestion) for VCPU Hotplug. It is a
non-ACPI
version and banks upon trapping KVM Host PSCI to user space (i.e. CPU_ON, CPU_OFF etc.) to let QEMU make the decisions i.e. whether CPUs could be made
online
or not.
Er, ... this is how it is expected to work. CPU_ON had 'Denied' added to allow firmware to apply some policy to which CPUs can be brought online.
sure, but we had not talked about using this on non-ACPI version (which of course does not looks like we can achieve)
There are two aspects to the ACPI changes. One is to tell the OS that the policy has changed, and it should try to bring CPUs online. This is required to make the use-case work. If the udev triggers don't occur when the policy change, this whole exercise is futile. The other is the online-capable bit in the MADT. This is because other operating systems may not be tolerant to PSCI returning errors. (although: it has always been able to do this).
I don't think you can remove the ACPI bits.
Agreed. Does not looks like without using any out-of-band notification like gRPC etc. but then we have already discussed the problems associated with this approach.