Messages in this thread | | | Subject | Re: [PATCH 7/8] cpufreq: Frequency invariant scheduler load-tracking support | From | Dietmar Eggemann <> | Date | Tue, 15 Mar 2016 19:13:46 +0000 |
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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.
> 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?
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