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Re: Xen C-state Issues

  • To: Elliott Mitchell <ehem+xen@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 23 Aug 2021 09:12:52 +0200
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  • Delivery-date: Mon, 23 Aug 2021 07:13:03 +0000
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On 21.08.2021 18:25, Elliott Mitchell wrote:
> ACPI C-state support might not see too much use, but it does see some.
> With Xen 4.11 and Linux kernel 4.19, I found higher C-states only got
> enabled for physical cores for which Domain 0 had a corresponding vCPU.
> On a machine where Domain 0 has 5 vCPUs, but 8 reported cores, the
> additional C-states would only be enabled on cores 0-4.
> This can be worked around by giving Domain 0 vCPUs equal to cores, but
> then offlining the extra vCPUs.  I'm guessing this is a bug with the
> Linux 4.19 xen_acpi_processor module.
> Appears Xen 4.14 doesn't work at all with Linux kernel 4.19's ACPI
> C-state support.  This combination is unable to enable higher C-states
> on any core.  Since Xen 4.14 and Linux 4.19 are *both* *presently*
> supported it seems patch(es) are needed somewhere for this combination.

Hmm, having had observed the same quite some time ago, I thought I had
dealt with these problems. Albeit surely not in Xen 4.11 or Linux 4.19.
Any chance you could check up-to-date versions of both Xen and Linux




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