Messages in this thread | | | From | Michael Turquette <> | Subject | Re: [PATCH 7/8] cpufreq: Frequency invariant scheduler load-tracking support | Date | Tue, 15 Mar 2016 13:19:17 -0700 |
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Quoting Dietmar Eggemann (2016-03-15 12:13:46) > Hi Mike, > > On 14/03/16 05:22, Michael Turquette wrote: > > From: Dietmar Eggemann <dietmar.eggemann@arm.com> > > > > Implements cpufreq_scale_freq_capacity() to provide the scheduler with a > > frequency scaling correction factor for more accurate load-tracking. > > > > The factor is: > > > > current_freq(cpu) << SCHED_CAPACITY_SHIFT / max_freq(cpu) > > > > In fact, freq_scale should be a struct cpufreq_policy data member. But > > this would require that the scheduler hot path (__update_load_avg()) would > > have to grab the cpufreq lock. This can be avoided by using per-cpu data > > initialized to SCHED_CAPACITY_SCALE for freq_scale. > > > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> > > Signed-off-by: Michael Turquette <mturquette+renesas@baylibre.com> > > --- > > I'm not as sure about patches 7 & 8, but I included them since I needed > > frequency invariance while testing. > > > > As mentioned by myself in 2014 and Rafael last month, the > > arch_scale_freq_capacity hook is awkward, because this behavior may vary > > within an architecture. > > > > I re-introduce Dietmar's generic cpufreq implementation of the frequency > > invariance hook in this patch, and change the preprocessor magic in > > sched.h to favor the cpufreq implementation over arch- or > > platform-specific ones in the next patch. > > Maybe it is worth mentioning that this patch is from EAS RFC5.2 > (linux-arm.org/linux-power.git energy_model_rfc_v5.2) which hasn't been > posted to LKML. The last EAS RFCv5 has the Frequency Invariant Engine > (FEI) based on the cpufreq notifier calls (cpufreq_callback, > cpufreq_policy_callback) in the ARM arch code.
Oops, my apologies. I got a little mixed up while developing these patches and I should have at least asked you about this one before posting.
I'm really quite happy to drop #7 and #8 if they are too contentious or if patch #7 is deemed as not-ready by you.
> > > If run-time selection of ops is needed them someone will need to write > > that code. > > Right now I see 3 different implementations of the FEI. 1) The X86 > aperf/mperf based one (https://lkml.org/lkml/2016/3/3/589), 2) This one > in cpufreq.c and 3) the one based on cpufreq notifiers in ARCH (ARM, > ARM64) code. > > I guess with sched_util we do need a solution for all platforms > (different archs, x86 w/ and w/o X86_FEATURE_APERFMPERF, ...). > > > I think that this negates the need for the arm arch hooks[0-2], and > > hopefully Morten and Dietmar can weigh in on this. > > It's true that we tried to get rid of the usage of the cpufreq callbacks > (cpufreq_callback, cpufreq_policy_callback) with this patch. Plus we > didn't want to implement it twice (for ARM and ARM64). > > But 2) would have to work for other ARCHs as well. Maybe as a fall-back > for X86 w/o X86_FEATURE_APERFMPERF feature?
That's what I had in mind. I guess that some day there will be a need to select implementations at run-time for both cpufreq (e.g. different cpufreq drivers might implement arch_scale_freq_capacity) and for the !CONFIG_CPU_FREQ case (e.g. different platforms might implement arch_scale_freq_capcity within the same arch).
The cpufreq approach seems the most generic, hence patch #8 to make it the default.
Regards, Mike
> > [...]
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