On 24.08.2021 07:37, Elliott Mitchell wrote: > On Mon, Aug 23, 2021 at 09:12:52AM +0200, Jan Beulich wrote: >> 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 >> (together)? > > I can believe you got this fixed, but the Linux fixes never got > backported. > > Of the two, higher C-states working with Linux 4.19 and Xen 4.11, but > not Linux 4.19 and Xen 4.14 is more concerning to me.
I'm afraid without you providing detail (full verbosity logs) and ideally checking with 4.15 or yet better -unstable it's going to be hard to judge whether that's a bug, and if so where it might sit. Jan
