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Message-ID: <ZtBvJk4MMCcF2SI8@gpd3> Date: Thu, 29 Aug 2024 14:52:54 +0200 From: Andrea Righi <andrea.righi@...ux.dev> To: "Gautham R. Shenoy" <gautham.shenoy@....com> Cc: Mario Limonciello <mario.limonciello@....com>, Mario Limonciello <superm1@...nel.org>, Borislav Petkov <bp@...en8.de>, Perry Yuan <perry.yuan@....com>, "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>, "Rafael J . Wysocki" <rafael@...nel.org>, "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>, "open list:ACPI" <linux-acpi@...r.kernel.org>, "open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>, changwoo@...lia.com, David Vernet <void@...ifault.com>, Tejun Heo <tj@...nel.org> Subject: Re: [PATCH 8/8] cpufreq: amd-pstate: Drop some uses of cpudata->hw_prefcore On Wed, Aug 28, 2024 at 08:27:44PM +0530, Gautham R. Shenoy wrote: > Hello Andrea, > > On Wed, Aug 28, 2024 at 08:20:50AM +0200, Andrea Righi wrote: > > On Wed, Aug 28, 2024 at 10:38:45AM +0530, Gautham R. Shenoy wrote: > > ... > > > > I had thought this was a malfunction in the behavior that it reflected the > > > > current status, not the hardware /capability/. > > > > > > > > Which one makes more sense for userspace? In my mind the most likely > > > > consumer of this information would be something a sched_ext based userspace > > > > scheduler. They would need to know whether the scheduler was using > > > > preferred cores; not whether the hardware supported it. > > > > > > The commandline parameter currently impacts only the fair sched-class > > > tasks since the preference information gets used only during > > > load-balancing. > > > > > > IMO, the same should continue with sched-ext, i.e. if the user has > > > explicitly disabled prefcore support via commandline, the no sched-ext > > > scheduler should use the preference information to make task placement > > > decisions. However, I would like to see what the sched-ext folks have > > > to say. Adding some of them to the Cc list. > > > > IMHO it makes more sense to reflect the real state of prefcore support > > from a "system" perspective, more than a "hardware" perspective, so if > > it's disabled via boot command line it should show disabled. > > > > From a user-space scheduler perspective we should be fine either way, as > > long as the ABI is clearly documented, since we also have access to > > /proc/cmdline and we would be able to figure out if the user has > > disabled it via cmdline (however, the preference is still to report the > > actual system status). > > Thank you for confirming this. > > > > > Question: having prefcore enabled affects also the value of > > scaling_max_freq? Like an `lscpu -e`, for example, would show a higher > > max frequency for the specific preferred cores? (this is another useful > > information from a sched_ext scheduler perspective). > > Since the scaling_max_freq is computed based on the boost-numerator, > at least from this patchset, the numerator would be the same across > all kinds of cores, and thus the scaling_max_freq reported will be the > same across all the cores. I see, so IIUC from user-space the most reliable way to detect the fastest cores is to check amd_pstate_highest_perf / amd_pstate_max_freq, right? I'm trying to figure out a way to abstract and generalize the concept of "fast cores" in sched_ext. Also, is this something that has changed recently? I see this on an AMD Ryzen Threadripper PRO 7975WX 32-Cores running a 6.8 kernel: $ uname -r 6.8.0-40-generic $ grep . /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_max_freq /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu1/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu2/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu3/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu4/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu5/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu6/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu7/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu8/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu9/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu10/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu11/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu12/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu13/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu14/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu15/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu16/cpufreq/cpuinfo_max_freq:6161000 /sys/devices/system/cpu/cpu17/cpufreq/cpuinfo_max_freq:6321000 /sys/devices/system/cpu/cpu18/cpufreq/cpuinfo_max_freq:6001000 /sys/devices/system/cpu/cpu19/cpufreq/cpuinfo_max_freq:6646000 /sys/devices/system/cpu/cpu20/cpufreq/cpuinfo_max_freq:5837000 /sys/devices/system/cpu/cpu21/cpufreq/cpuinfo_max_freq:6482000 /sys/devices/system/cpu/cpu22/cpufreq/cpuinfo_max_freq:5517000 /sys/devices/system/cpu/cpu23/cpufreq/cpuinfo_max_freq:5677000 /sys/devices/system/cpu/cpu24/cpufreq/cpuinfo_max_freq:6966000 /sys/devices/system/cpu/cpu25/cpufreq/cpuinfo_max_freq:7775000 /sys/devices/system/cpu/cpu26/cpufreq/cpuinfo_max_freq:6806000 /sys/devices/system/cpu/cpu27/cpufreq/cpuinfo_max_freq:7775000 /sys/devices/system/cpu/cpu28/cpufreq/cpuinfo_max_freq:7130000 /sys/devices/system/cpu/cpu29/cpufreq/cpuinfo_max_freq:7451000 /sys/devices/system/cpu/cpu30/cpufreq/cpuinfo_max_freq:7290000 /sys/devices/system/cpu/cpu31/cpufreq/cpuinfo_max_freq:7611000 /sys/devices/system/cpu/cpu32/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu33/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu34/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu35/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu36/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu37/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu38/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu39/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu40/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu41/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu42/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu43/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu44/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu45/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu46/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu47/cpufreq/cpuinfo_max_freq:5352000 /sys/devices/system/cpu/cpu48/cpufreq/cpuinfo_max_freq:6161000 /sys/devices/system/cpu/cpu49/cpufreq/cpuinfo_max_freq:6321000 /sys/devices/system/cpu/cpu50/cpufreq/cpuinfo_max_freq:6001000 /sys/devices/system/cpu/cpu51/cpufreq/cpuinfo_max_freq:6646000 /sys/devices/system/cpu/cpu52/cpufreq/cpuinfo_max_freq:5837000 /sys/devices/system/cpu/cpu53/cpufreq/cpuinfo_max_freq:6482000 /sys/devices/system/cpu/cpu54/cpufreq/cpuinfo_max_freq:5517000 /sys/devices/system/cpu/cpu55/cpufreq/cpuinfo_max_freq:5677000 /sys/devices/system/cpu/cpu56/cpufreq/cpuinfo_max_freq:6966000 /sys/devices/system/cpu/cpu57/cpufreq/cpuinfo_max_freq:7775000 /sys/devices/system/cpu/cpu58/cpufreq/cpuinfo_max_freq:6806000 /sys/devices/system/cpu/cpu59/cpufreq/cpuinfo_max_freq:7775000 /sys/devices/system/cpu/cpu60/cpufreq/cpuinfo_max_freq:7130000 /sys/devices/system/cpu/cpu61/cpufreq/cpuinfo_max_freq:7451000 /sys/devices/system/cpu/cpu62/cpufreq/cpuinfo_max_freq:7290000 /sys/devices/system/cpu/cpu63/cpufreq/cpuinfo_max_freq:7611000 Thanks, -Andrea
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