linux-kernel - Re: [PATCH 0/3] per cpu resume latency

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Date:   Thu, 5 Jan 2017 23:48:34 +0800
From:   Alex Shi <alex.shi@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        vincent.guittot@...aro.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 0/3] per cpu resume latency

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
>