linux-kernel - Re: [PATCHv3 0/3] cpuidle: teo: Fixing utilization and intercept logic

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Date: Fri, 28 Jun 2024 21:06:56 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Christian Loehle <christian.loehle@....com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, rafael@...nel.org, 
	vincent.guittot@...aro.org, qyousef@...alina.io, peterz@...radead.org, 
	daniel.lezcano@...aro.org, ulf.hansson@...aro.org, anna-maria@...utronix.de, 
	dsmythies@...us.net, kajetan.puchalski@....com, lukasz.luba@....com, 
	dietmar.eggemann@....com
Subject: Re: [PATCHv3 0/3] cpuidle: teo: Fixing utilization and intercept logic

On Fri, Jun 28, 2024 at 12:02 PM Christian Loehle
<christian.loehle@....com> wrote:
>
> Hi all,
> so my investigation into teo lead to the following fixes.
>
> 1/3:
> As discussed the utilization threshold is too high while
> there are benefits in certain workloads, there are quite a few
> regressions, too. Revert the Util-awareness patch.
> This in itself leads to regressions, but part of it can be offset
> by the later patches.
> See
> https://lore.kernel.org/lkml/CAKfTPtA6ZzRR-zMN7sodOW+N_P+GqwNv4tGR+aMB5VXRT2b5bg@mail.gmail.com/
> 2/3:
> Remove the 'recent' intercept logic, see my findings in:
> https://lore.kernel.org/lkml/0ce2d536-1125-4df8-9a5b-0d5e389cd8af@arm.com/
> I haven't found a way to salvage this properly, so I removed it.
> The regular intercept seems to decay fast enough to not need this, but
> we could change it if that turns out that we need this to be faster in
> ramp-up and decaying.
> 3/3:
> The rest of the intercept logic had issues, too.
> See the commit.
>
> Happy for anyone to take a look and test as well.
>
> Some numbers for context, comparing:
> - IO workload (intercept heavy).
> - Timer workload very low utilization (check for deepest state)
> - hackbench (high utilization)
> - Geekbench 5 on Pixel6 (high utilization)
> Tests 1 to 3 are on RK3399 with CONFIG_HZ=100.
> target_residencies: 1, 900, 2000
>
> 1. IO workload, 5 runs, results sorted, in read IOPS.
> fio --minimal --time_based --name=fiotest --filename=/dev/nvme0n1 --runtime=30 --rw=randread --bs=4k --ioengine=psync --iodepth=1 --direct=1 | cut -d \; -f 8;
>
> teo fixed v2:
> /dev/nvme0n1
> [4599, 4658, 4692, 4694, 4720]
> /dev/mmcblk2
> [5700, 5730, 5735, 5747, 5977]
> /dev/mmcblk1
> [2052, 2054, 2066, 2067, 2073]
>
> teo mainline:
> /dev/nvme0n1
> [3793, 3825, 3846, 3865, 3964]
> /dev/mmcblk2
> [3831, 4110, 4154, 4203, 4228]
> /dev/mmcblk1
> [1559, 1564, 1596, 1611, 1618]
>
> menu:
> /dev/nvme0n1
> [2571, 2630, 2804, 2813, 2917]
> /dev/mmcblk2
> [4181, 4260, 5062, 5260, 5329]
> /dev/mmcblk1
> [1567, 1581, 1585, 1603, 1769]
>
>
> 2. Timer workload (through IO for my convenience 😉 )
> Results in read IOPS, fio same as above.
> echo "0 2097152 zero" | dmsetup create dm-zeros
> echo "0 2097152 delay /dev/mapper/dm-zeros 0 50" | dmsetup create dm-slow
> (Each IO is delayed by timer of 50ms, should be mostly in state2, for 5s total)
>
> teo fixed v2:
> idle_state time
> 2.0     4.807025
> -1.0    0.219766
> 0.0     0.072007
> 1.0     0.169570
>
> 3199 cpu_idle total
> 38 cpu_idle_miss
> 31 cpu_idle_miss above
> 7 cpu_idle_miss below
>
> teo mainline:
> idle_state time
> 1.0     4.897942
> -1.0    0.095375
> 0.0     0.253581
>
> 3221 cpu_idle total
> 1269 cpu_idle_miss
> 22 cpu_idle_miss above
> 1247 cpu_idle_miss below
>
> menu:
> idle_state time
> 2.0     4.295546
> -1.0    0.234164
> 1.0     0.356344
> 0.0     0.401507
>
> 3421 cpu_idle total
> 129 cpu_idle_miss
> 52 cpu_idle_miss above
> 77 cpu_idle_miss below
>
> Residencies:
> teo mainline isn't in state2 at all, teo fixed is more in state2 than menu, but
> both are in state2 the vast majority of the time as expected.
>
> tldr: overall teo fixed spends more time in state2 while having
> fewer idle_miss than menu.
> teo mainline was just way too aggressive at selecting shallow states.
>
> 3. Hackbench, 5 runs
> for i in $(seq 0 4); do hackbench -l 100 -g 100 ; sleep 1; done
>
> teo fixed v2:
> Time: 4.937
> Time: 4.898
> Time: 4.871
> Time: 4.833
> Time: 4.898
>
> teo mainline:
> Time: 4.945
> Time: 5.021
> Time: 4.927
> Time: 4.923
> Time: 5.137
>
> menu:
> Time: 4.964
> Time: 4.847
> Time: 4.914
> Time: 4.841
> Time: 4.800
>
> tldr: all comparable, teo mainline slightly worse
>
> 4. Geekbench 5 (multi-core) on Pixel6
> (Device is cooled for each iteration separately)
> teo mainline:
> 3113, 3068, 3079
> mean 3086.66
>
> teo revert util-awareness:
> 2947, 2941, 2952
> mean 2946.66 (-4.54%)
>
> teo fixed v2:
> 3032, 3066, 3019
> mean 3039 (-1.54%)
>
>
> Changes since v2:
> - Reworded commits according to Dietmar's comments
> - Dropped the KTIME_MAX as hit part from 3/3 according to Dietmar's
> remark.
>
> Changes since v1:
> - Removed all non-fixes.
> - Do a full revert of Util-awareness instead of increasing thresholds.
> - Address Dietmar's comments.
> https://lore.kernel.org/linux-kernel/20240606090050.327614-2-christian.loehle@arm.com/T/
>
> Kind Regards,
> Christian
>
> Christian Loehle (3):
>   Revert: "cpuidle: teo: Introduce util-awareness"
>   cpuidle: teo: Remove recent intercepts metric
>   cpuidle: teo: Don't count non-existent intercepts
>
>  drivers/cpuidle/governors/teo.c | 189 +++++---------------------------
>  1 file changed, 27 insertions(+), 162 deletions(-)
>
> --

Patches [1-2/3] have been applied as 6.11 material.

Patch [3/3] looks like it may be improved slightly, see my reply to that patch.

Thanks!