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SubjectRe: [PATCH 0/3] per cpu resume latency
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Sorry for missing the mailing list.

Add linux-kernel and linux-pm.


On 01/05/2017 11:29 PM, Alex Shi wrote:
> cpu_dma_latency is designed to keep all cpu awake from deep c-state.
> That is good keep system with short response latency. But sometime we
> don't need all cpu power especially in a more and more multi-core day.
> So set all cpu restless that lead to a big power waste.
>
> A better way is to keep the short cpu response latency on needed cpu,
> while let other unnecesscary cpus go to deep idle. That is this
> patchset. We just use the pm_qos_resume_latency on cpu. Giving the
> short cpu latency on appointed cpu via setting value on
> /sys/devices/system/cpu/cpuX/power/pm_qos_resume_latency_us
> We can set we wanted latency value according to the value of
> /sys/devices/system/cpu/cpuX/cpuidle/stateX/latency. to just a bit
> less related state's latency value. Then cpu can get to this state or
> higher.
>
> Here is some testing data on my dragonboard 410c, the latency of state1
> is 280us. It has 4 cores.
>
> Benchmark: cyclictest -t 1 -n -i 10000 -l 1000 -q --latency=10000
>
> without the patch:
> Latency (us) Min: 87 Act: 209 Avg: 205 Max: 239
> With the patch and cpu0/power/pm_qos_resume_latency_us is lower than
> 280us, like set to 279
> benchmark result on cpu0:
> Latency (us) Min: 82 Act: 91 Avg: 95 Max: 110
> In repeat testing, the Avg latency always drop to half of vanilla kernel
> value, as well as Max latency value, although sometime the Max latency
> is similar with vanilla kernel.
>
> Also we could use the cpu_dma_latency to get the similar short latency.
> But 'idlestate' show all cpu are restless. Here is the idle status
> compression between cpu_dma_latency and this feature:
>
> To record idlestate
> #./idlestat --trace -t 10 -f /tmp/mytracepmlat -p -c -w -- cyclictest -t 1 -n -i 10000 -l 1000 -q --latency=10000
>
> To compare the idle state, the 'total' colum show cpu1~3 nearly stay
> in WFI state with cpu_dma_latency. but w/ my patch, they can get about
> 10 second sleep in 'spc' state.
> # ./idlestat --import -f /tmp/mytracepmlat -b /tmp/mytrace -r comparison
> Log is 10.055305 secs long with 7514 events
> Log is 10.055370 secs long with 7545 events
> --------------------------------------------------------------------------------
> | C-state | min | max | avg | total | hits | over | under |
> --------------------------------------------------------------------------------
> | clusterA |
> --------------------------------------------------------------------------------
> | WFI | 2us | 12.88ms | 4.18ms | 9.76s | 2334 | 0 | 0 |
> | | -2us | -14.4ms | -17us | -72.5ms | -8 | 0 | 0 |
> --------------------------------------------------------------------------------
> | cpu0 |
> --------------------------------------------------------------------------------
> | WFI | 3us | 100.98ms | 26.81ms | 10.03s | 374 | 0 | 0 |
> | | -1us | -1us | -350us | +5.0ms | +5 | 0 | 0 |
> --------------------------------------------------------------------------------
> | cpu1 |
> --------------------------------------------------------------------------------
> | WFI | 280us | 3.96ms | 1.96ms | 19.64ms | 10 | 0 | 5 |
> | | +221us | -891.7ms | -9.1ms | -9.9s | -889 | 0 | 0 |
> | spc | 234us | 19.71ms | 9.79ms | 9.91s | 1012 | 4 | 0 |
> | | +167us | +17.9ms | +8.6ms | +9.9s | +1009 | +1 | 0 |
> --------------------------------------------------------------------------------
> | cpu2 |
> --------------------------------------------------------------------------------
> | WFI | 86us | 1.01ms | 637us | 1.91ms | 3 | 0 | 0 |
> | | -16us | -26.5ms | -8.8ms | -10.0s | -1057 | 0 | 0 |
> | spc | 930us | 47.67ms | 10.05ms | 9.92s | 987 | 2 | 0 |
> | | -1.4ms | +43.7ms | +6.9ms | +9.9s | +985 | +2 | 0 |
> --------------------------------------------------------------------------------
> | cpu3 |
> --------------------------------------------------------------------------------
> | WFI | 0us | 0us | 0us | 0us | 0 | 0 | 0 |
> | | | -4.0s | -152.1ms | -10.0s | -66 | 0 | 0 |
> | spc | 420us | 3.50s | 913.74ms | 10.05s | 11 | 3 | 0 |
> | | -891us | +3.5s | +911.0ms | +10.0s | +8 | +1 | 0 |
> --------------------------------------------------------------------------------
>
>
> Thanks
> Alex
>

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