Re: [RFC PATCH v7 11/23] sched/fair: core wide cfs task priority comparison

[Joel Fernandes <joel@joelfernandes.org>]

On Tue, Sep 22, 2020 at 09:46:22PM -0400, Joel Fernandes wrote:
> On Fri, Aug 28, 2020 at 11:29:27PM +0200, Peter Zijlstra wrote:
> > 
> > 
> > This is still a horrible patch..
> 
> Hi Peter,
> I wrote a new patch similar to this one and it fares much better in my tests,
> it is based on Aaron's idea but I do the sync only during force-idle, and not
> during enqueue. Also I yanked the whole 'core wide min_vruntime' crap. There
> is a regressing test which improves quite a bit with my patch (results below):
> 
> Aaron, Vineeth, Chris any other thoughts? This patch is based on Google's
> 4.19 device kernel so will require some massaging to apply to mainline/v7
> series. I will provide an updated patch later based on v7 series.
> 
> (Works only for SMT2, maybe we can generalize it more..)
> --------8<-----------
> 
> From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
> Subject: [PATCH] sched: Sync the min_vruntime of cores when the system enters
>  force-idle
> 
> This patch provides a vruntime based way to compare two cfs task's priority, be
> it on the same cpu or different threads of the same core.
> 
> It is based on Aaron Lu's patch with some important differences. Namely,
> the vruntime is sync'ed only when the CPU goes into force-idle. Also I removed
> the notion of core-wide min_vruntime.
> 
> Also I don't care how long a cpu in a core is force idled,  I do my sync
> whenever the force idle starts essentially bringing both SMTs to a common time
> base. After that point, selection can happen as usual.
> 
> When running an Android audio test, with patch the perf sched latency output:
> 
> -----------------------------------------------------------------------------------------------------------------
> Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at       |
> -----------------------------------------------------------------------------------------------------------------
> FinalizerDaemon:(2)   |     23.969 ms |      969 | avg:    0.504 ms | max:  162.020 ms | max at:   1294.327339 s
> HeapTaskDaemon:(3)    |   2421.287 ms |     4733 | avg:    0.131 ms | max:   96.229 ms | max at:   1302.343366 s
> adbd:(3)              |      6.101 ms |       79 | avg:    1.105 ms | max:   84.923 ms | max at:   1294.431284 s
> 
> Without this patch and with Aubrey's initial patch (in v5 series), the max delay looks much better:
> 
> -----------------------------------------------------------------------------------------------------------------
> Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at       |
> -----------------------------------------------------------------------------------------------------------------
> HeapTaskDaemon:(2)    |   2602.109 ms |     4025 | avg:    0.231 ms | max:   19.152 ms | max at:    522.903934 s
> surfaceflinger:7478   |     18.994 ms |     1206 | avg:    0.189 ms | max:   17.375 ms | max at:    520.523061 s
> ksoftirqd/3:30        |      0.093 ms |        5 | avg:    3.328 ms | max:   16.567 ms | max at:    522.903871 s

I messed up the change log, just to clarify - the first result is without
patch (bad) and the second result is with patch (good).

thanks,

 - Joel