From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id BDA322141B5 for ; Fri, 11 Oct 2024 12:52:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728651146; cv=none; b=FGRpuEFIbL8jruuwMlC5M65UKPBQcX7/YJoZ2+zkuDk1/eqiWKgR/6IFchW+dcHoarkyCEp5Al4osIy2NBMilW//5i8l0aTym+x/Y9VIYZ0J0TD/QEdj/IsdqOlsugi1LeDKTu7djO+AJ93ohgVn1OP8N0nu0B4ClO9h7r5odoQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728651146; c=relaxed/simple; bh=Mkx14mAjHPqOtseLvwEdoAfTDmF/gsjlSafOH2m7cAs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=BKaj7FbyGhj3x8WGRWC11VkHoiXauFh3QRV4sDYTukM15XR0rW1izKxPYTwuP3N7alpFIQyqsWmLnwikfrbJbhchp4AgmmvgN2Nuyc9eoN/niVjzT0zKZRlokRXfNgyuRJ1JmD1slcgpij571m17/B4alY96P+4w4UnRk+iQ1cA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6B458497; Fri, 11 Oct 2024 05:52:53 -0700 (PDT) Received: from [10.34.129.34] (e126645.nice.arm.com [10.34.129.34]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E8623F64C; Fri, 11 Oct 2024 05:52:20 -0700 (PDT) Message-ID: <59b31e93-9784-493d-8c85-10e07aabd86b@arm.com> Date: Fri, 11 Oct 2024 14:52:18 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 4/5] sched/fair: Use EAS also when overutilized To: Vincent Guittot Cc: Christian Loehle , qyousef@layalina.io, hongyan.xia2@arm.com, mingo@redhat.com, peterz@infradead.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, lukasz.luba@arm.com, vschneid@redhat.com, mgorman@suse.de, bsegall@google.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, juri.lelli@redhat.com References: <20240830130309.2141697-1-vincent.guittot@linaro.org> <20240830130309.2141697-5-vincent.guittot@linaro.org> <64ed0fb8-12ea-4452-9ec2-7ad127b65529@arm.com> <66583e86-e2a7-4e4f-bd45-40ea2d4a21df@arm.com> Content-Language: en-US From: Pierre Gondois In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Hello Vincent, On 10/9/24 10:53, Vincent Guittot wrote: > Hi Pierre, > > On Mon, 7 Oct 2024 at 09:03, Pierre Gondois wrote: >> >> Hello Vincent, >> >> Sorry for the delay: >> >> On 9/25/24 15:28, Vincent Guittot wrote: >>> On Thu, 19 Sept 2024 at 10:26, Pierre Gondois wrote: >>>> >>>> Hello Vincent, >>>> I tried this patch on a Pixel 6 (8 CPUs, 4 little, 2 mid, 2 big) >>>> with patches 1-4/5 using these workloads: >>>> --- >>>> A. >>>> a. 8 tasks at 2%/5%/10% during 1s >>>> b. 1 task: >>>> - sleeping during 0.3s >>>> - at 100% during 0.3s >>>> - sleeping during 0.3s >>>> >>>> b. is used to reach the overutilized state during a limited amount of time. >>>> EAS is then operating, then the load balancer does the task placement, then EAS >>>> is operating again. >>>> >>>> B. >>>> a. 8 tasks at 2%/5%/10% during 1s >>>> b. 1 task: >>>> - at 100% during 1s >>>> >>>> --- >>>> I'm seeing the energy consumption increase in some cases. This seems to be >>>> due to feec() migrating tasks more often than what the load balancer does >>>> for this workload. This leads to utilization 'spikes' and then frequency >>>> 'spikes', increasing the overall energy consumption. >>>> This is not entirely related to this patch though,, as the task placement seems >>>> correct. I.e. feec() effectively does an optimal placement given the EM and >>>> task utilization. The task placement is just a bit less stable than with >>>> the load balancer. >>> >>> Would patch 5 help to keep things better placed ? in particular if >>> task b is misplaced at some point because of load balance ? >> >> I assume so, it would require more testing on my side >> >>> >>> I agree that load balance might still contribute to migrate task in a >>> not energy efficient way >>> >>>> >>>> --- >>>> Regarding hackbench, I've reproduced the test you've run on the same Pixel6. >>>> I have CONFIG_SCHED_CLUSTER enabled, which allows having a sched domain for >>>> each little/mid/big CPUs (without the config, these group would no exist). >>> >>> Why did you do this ? All cpus are expected to be in same sched domain >>> as they share their LLC >> >> I did this to observe the loa balancer a bit more carefully while reviewing >> the first patch: >> sched/fair: Filter false overloaded_group case for EAS >> I've let this configuration, but effectively this should not bring anything more. >> >> >>> >>>> >>>> I see an important regression in the result. >>>> I replaced the condition to run feec() through select_task_rq_fair() by: >>>> if (get_rd_overloaded(cpu_rq(cpu)->rd) == 0)) { >>> >>> overloaded is enable when more than 1 task runs on a cpu whatever the >>> utilization >> >> Yes right, this idea has little sense. >> >>> >>>> new_cpu = find_energy_efficient_cpu(p, prev_cpu); >>>> ... >>>> } >>>> and obtained better results. >>>> >>>> Indeed, for such intensive workload: >>>> - EAS would not have any energy benefit, so better prioritize performance >>>> (as Christian mentioned) >>>> - EAS would not be able to find a fitting CPU, so running feec() should be >>>> avoided >>>> - as you mention in the commit message, shuffling tasks when one CPU becomes >>>> momentarily overutilized is inefficient energy-wise (even though I don't have >>>> the numbers, it should make sense). >>>> So detecting when the system is overloaded should be a better compromise I >>>> assume. The condition in sched_balance_find_src_group() to let the load balancer >>>> operate might also need to be updated. >>>> >>>> Note: >>>> - base: with patches 1-4/5 >>>> - _ou: run feec() when not overutilized >>>> - _ol: run feec() when not overloaded >>>> - mean: hackbench execution time in s. >>>> - delta: negative is better. Value is in percentage. >>> >>> Could you share your command line ? As explained in the cover letter I >>> have seen some perf regressions but not in the range that you have >>> below >>> >>> What is your base ? tip/sched/core ? >> >> I am working on a Pixel6, with a branch based on v6.8 with some scheduler patches >> to be able to apply your patches cleanly. > > TBH, I'm always cautious with those kind of frankenstein kernel > especially with all changes that have happened on the scheduler since > v6.8 compared to tip/sched/core Yes I understand, I'll re-test it on a Juno with a newer kernel. > >> >> The mapping id -> command line is as: > > Thanks for the commands details, I'm going to have a look > >> (1) hackbench -l 5120 -g 1 >> (2) hackbench -l 1280 -g 4 >> (3) hackbench -l 640 -g 8 >> (4) hackbench -l 320 -g 16 >> >> (5) hackbench -p -l 5120 -g 1 >> (6) hackbench -p -l 1280 -g 4 >> (7) hackbench -p -l 640 -g 8 >> (8) hackbench -p -l 320 -g 16 >> >> (9) hackbench -T -l 5120 -g 1 >> (10) hackbench -T -l 1280 -g 4 >> (11) hackbench -T -l 640 -g 8 >> (12) hackbench -T -l 320 -g 16 >> >> (13) hackbench -T -p -l 5120 -g 1 >> (14) hackbench -T -p -l 1280 -g 4 >> (15) hackbench -T -p -l 640 -g 8 >> (16) hackbench -T -p -l 320 -g 16 >> >> >>> >>>> ┌─────┬───────────┬──────────┬─────────┬──────────┬─────────┬──────────┬──────────┬──────────┐ >>>> │ id ┆ mean_base ┆ std_base ┆ mean_ou ┆ std_ou ┆ mean_ol ┆ std_ol ┆ delta_ou ┆ delta_ol │ >>>> ╞═════╪═══════════╪══════════╪═════════╪══════════╪═════════╪══════════╪══════════╪══════════╡ >>>> │ 1 ┆ 1.9786 ┆ 0.04719 ┆ 3.0856 ┆ 0.122209 ┆ 2.1734 ┆ 0.045203 ┆ 55.95 ┆ 9.85 │ > > I might have misunderstood your results above last time. > mean_base results include patches 1 to 4 and mean_ou revert patch 4. > Does it mean that it is 55% better with patch 4 ? I originally thought > there was a regression with patch 4 but I'm not sure that I understood > correctly after re reading the table. The columns are: - the _base configuration disables EAS/feec() when in the overutilized state, i.e. patches 1-3 are applied. - the _ou configuration keeps running EAS/feec() when in the overutilized state i.e. patches 1-4 are applied - the _ol configuration should be ignored as previously established > >>>> │ 2 ┆ 1.8991 ┆ 0.019768 ┆ 2.6672 ┆ 0.135266 ┆ 1.98875 ┆ 0.055132 ┆ 40.45 ┆ 4.72 │ >>>> │ 3 ┆ 1.9053 ┆ 0.014795 ┆ 2.5761 ┆ 0.141693 ┆ 2.06425 ┆ 0.045901 ┆ 35.21 ┆ 8.34 │ >>>> │ 4 ┆ 1.9586 ┆ 0.023439 ┆ 2.5823 ┆ 0.110399 ┆ 2.0955 ┆ 0.053818 ┆ 31.84 ┆ 6.99 │ >>>> │ 5 ┆ 1.746 ┆ 0.055676 ┆ 3.3437 ┆ 0.279107 ┆ 1.88 ┆ 0.038184 ┆ 91.51 ┆ 7.67 │ >>>> │ 6 ┆ 1.5476 ┆ 0.050131 ┆ 2.6835 ┆ 0.140497 ┆ 1.5645 ┆ 0.081644 ┆ 73.4 ┆ 1.09 │ >>>> │ 7 ┆ 1.4562 ┆ 0.062457 ┆ 2.3568 ┆ 0.119213 ┆ 1.48425 ┆ 0.06212 ┆ 61.85 ┆ 1.93 │ >>>> │ 8 ┆ 1.3554 ┆ 0.031757 ┆ 2.0609 ┆ 0.112869 ┆ 1.4085 ┆ 0.036601 ┆ 52.05 ┆ 3.92 │ >>>> │ 9 ┆ 2.0391 ┆ 0.035732 ┆ 3.4045 ┆ 0.277307 ┆ 2.2155 ┆ 0.019053 ┆ 66.96 ┆ 8.65 │ >>>> │ 10 ┆ 1.9247 ┆ 0.056472 ┆ 2.6605 ┆ 0.119417 ┆ 2.02775 ┆ 0.05795 ┆ 38.23 ┆ 5.35 │ >>>> │ 11 ┆ 1.8923 ┆ 0.038222 ┆ 2.8113 ┆ 0.120623 ┆ 2.089 ┆ 0.025259 ┆ 48.57 ┆ 10.39 │ >>>> │ 12 ┆ 1.9444 ┆ 0.034856 ┆ 2.6675 ┆ 0.219585 ┆ 2.1035 ┆ 0.076514 ┆ 37.19 ┆ 8.18 │ >>>> │ 13 ┆ 1.7107 ┆ 0.04874 ┆ 3.4443 ┆ 0.154481 ┆ 1.8275 ┆ 0.036665 ┆ 101.34 ┆ 6.83 │ >>>> │ 14 ┆ 1.5565 ┆ 0.056595 ┆ 2.8241 ┆ 0.158643 ┆ 1.5515 ┆ 0.040813 ┆ 81.44 ┆ -0.32 │ >>>> │ 15 ┆ 1.4932 ┆ 0.085256 ┆ 2.6841 ┆ 0.135623 ┆ 1.50475 ┆ 0.028336 ┆ 79.75 ┆ 0.77 │ >>>> │ 16 ┆ 1.4263 ┆ 0.067666 ┆ 2.3971 ┆ 0.145928 ┆ 1.414 ┆ 0.061422 ┆ 68.06 ┆ -0.86 │ >>>> └─────┴───────────┴──────────┴─────────┴──────────┴─────────┴──────────┴──────────┴──────────┘ >>>> >>>> On 9/17/24 22:24, Christian Loehle wrote: >>>>> On 8/30/24 14:03, Vincent Guittot wrote: >>>>>> Keep looking for an energy efficient CPU even when the system is >>>>>> overutilized and use the CPU returned by feec() if it has been able to find >>>>>> one. Otherwise fallback to the default performance and spread mode of the >>>>>> scheduler. >>>>>> A system can become overutilized for a short time when workers of a >>>>>> workqueue wake up for a short background work like vmstat update. >>>>>> Continuing to look for a energy efficient CPU will prevent to break the >>>>>> power packing of tasks. >>>>>> >>>>>> Signed-off-by: Vincent Guittot >>>>>> --- >>>>>> kernel/sched/fair.c | 2 +- >>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>>>> index 2273eecf6086..e46af2416159 100644 >>>>>> --- a/kernel/sched/fair.c >>>>>> +++ b/kernel/sched/fair.c >>>>>> @@ -8505,7 +8505,7 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) >>>>>> cpumask_test_cpu(cpu, p->cpus_ptr)) >>>>>> return cpu; >>>>>> >>>>>> - if (!is_rd_overutilized(this_rq()->rd)) { >>>>>> + if (sched_energy_enabled()) { >>>>>> new_cpu = find_energy_efficient_cpu(p, prev_cpu); >>>>>> if (new_cpu >= 0) >>>>>> return new_cpu; >>>>> >>>>> Super quick testing on pixel6: >>>>> for i in $(seq 0 6); do /data/local/tmp/hackbench -l 500 -g 100 | grep Time; sleep 60; done >>>>> with patch 5/5 only: >>>>> Time: 19.433 >>>>> Time: 19.657 >>>>> Time: 19.851 >>>>> Time: 19.789 >>>>> Time: 19.857 >>>>> Time: 20.092 >>>>> Time: 19.973 >>>>> >>>>> mainline: >>>>> Time: 18.836 >>>>> Time: 18.718 >>>>> Time: 18.781 >>>>> Time: 19.015 >>>>> Time: 19.061 >>>>> Time: 18.950 >>>>> Time: 19.166 >>>>> >>>>> >>>>> The reason we didn't always have this enabled is the belief that >>>>> this costs us too much performance in scenarios we most need it >>>>> while at best making subpar EAS decisions anyway (in an >>>>> overutilized state). >>>>> I'd be open for questioning that, but why the change of mind? >>>>> And why is this necessary in your series if the EAS selection >>>>> isn't 'final' (until the next sleep) anymore (Patch 5/5)? >>>>>