Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Wed, 18 Jul 2018 12:51:34 +0200 | Subject | Re: [PATCH] cpufreq: intel_pstate: Register when ACPI PCCH is present |
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On Wed, Jul 18, 2018 at 12:43 PM, Andreas Herrmann <aherrmann@suse.com> wrote: > On Tue, Jul 17, 2018 at 08:06:54PM +0200, Rafael J. Wysocki wrote: >> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> >> Currently, intel_pstate doesn't load if _PSS is not present on >> HP Proliant systems, because it expects the firmware to take over >> CPU performance scaling in that case. However, if ACPI PCCH is >> present, the firmware expects the kernel to use it for CPU >> performance scaling and the pcc-cpufreq driver is loaded for that. >> >> Unfortunately, the firmware interface used by that driver is not >> scalable for fundamental reasons, so pcc-cpufreq is way suboptimal >> on systems with more than just a few CPUs. In fact, it is better to >> avoid using it at all. >> >> For this reason, modify intel_pstate to look for ACPI PCCH if _PSS >> is not present and register if it is there. Also prevent the >> pcc-cpufreq driver from trying to initialize if intel_pstate has >> been registered already. >> >> Fixes: fbbcdc0744da (intel_pstate: skip the driver if ACPI has power mgmt option) >> Reported-by: Andreas Herrmann <aherrmann@suse.com> >> Reviewed-by: Andreas Herrmann <aherrmann@suse.com> >> Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> >> --- >> >> This is a replacement for https://patchwork.kernel.org/patch/10530091/ >> >> In addition to the intel_pstate changes in the above, it also >> prevents pcc-cpufreq from trying to initialize (which will fail >> ultimately, but may confuse the firmware in the meantime). >> >> Andreas, please test this one and let me know if it still works for you. > > Done that (with system in "Dynamic Power Savings Mode"). It still > works and system was stable.
Thanks!
> FYI, as a sniff test I've run a kernbench test. I now repeat the test > with system switched to "OS control mode". Just in case -- if there > was interference with platform code while system was in "Dynamic Power > Savings Mode" (significantly affecting performance) I might spot it > this way.
I'd rather not expect performance to be affected by this, but power very well may be affected.
Anyway, good idea!
Cheers, Rafael
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