linux-kernel - Re: [PATCH v2 6/8] sched/idle: Move busy

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Date:   Tue, 18 May 2021 09:30:24 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Aubrey Li <aubrey.li@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Parth Shah <parth@...ux.ibm.com>
Subject: Re: [PATCH v2 6/8] sched/idle: Move busy_cpu accounting to idle
 callback

* Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-18 08:59:00]:

> On 5/17/21 8:57 PM, Srikar Dronamraju wrote:
> > * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-17 20:48:46]:
> > 
> >> On 5/17/21 6:40 PM, Srikar Dronamraju wrote:
> >>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-14 12:11:50]:
> >>>
> >>>> On 5/13/21 3:31 PM, Srikar Dronamraju wrote:
> >>>>> * Aubrey Li <aubrey.li@...ux.intel.com> [2021-05-12 16:08:24]:
> >>>>>> On 5/7/21 12:45 AM, Srikar Dronamraju wrote:
> >>>
> >>> <snip>
> >>>
> >>>>>> Also, for those frequent context-switching tasks with very short idle,
> >>>>>> it's expensive for scheduler to mark idle/busy every time, that's why
> >>>>>> my patch only marks idle every time and marks busy ratelimited in
> >>>>>> scheduler tick.
> >>>>>>
> >>>>>
> >>>>> I have tried few tasks with very short idle times and updating nr_busy
> >>>>> everytime, doesnt seem to be impacting. Infact, it seems to help in picking
> >>>>> the idler-llc more often.
> >>>>>
> >>>>
> >>>> How many CPUs in your LLC?
> >>>
> >>> I have tried with X86, 48 CPUs, 2 nodes, each having 24 CPUs in LLC
> >>> +
> >>> POWER10, Multiple CPUs with 4 CPUs in LLC
> >>> +
> >>> POWER9, Multiple CPUs with 8 CPUs in LLC
> >>>
> >>>>
> >>>> This is a system with 192 CPUs, 4 nodes and each node has 48 CPUs in LLC
> >>>> domain.
> >>>>
> >>>
> >>> Okay,
> >>>
> >>>> It looks like for netperf both TCP and UDP cases have the notable change
> >>>> under 2 x overcommit, it may be not interesting though.
> >>>>
> >>>>
> >>>
> >>> I believe the extra load on this 24 core LLC could be because we may end up
> >>> trying to set the idle-core, even when there is no idle core available.
> >>>
> >>> If possible, can you please give a try with v3 with the call to
> >>> set_next_idle_core commented out?
> >>>
> >>>
> >>
> >> v3 seems not be applicable on tip/sched/core 915a2bc3c6b7?
> > 
> > I had applied on top of 2ea46c6fc9452ac100ad907b051d797225847e33
> > which was tag: sched-core-2021-04-28
> > 
> > The only conflict you get on today's tip is Gautham's one line patch.
> > Gautham's patch replaced 'this' with 'target'.
> > 
> > The 2nd patch does away with that line
> > 
> 
> This is v3. It looks like hackbench gets better. And netperf still has
> some notable changes under 2 x overcommit cases.
> 

Thanks Aubrey for the results. netperf (2X) case does seem to regress.
I was actually expecting the results to get better with overcommit.
Can you confirm if this was just v3 or with v3 + set_next_idle_core
disabled?

> 
> hackbench (48 tasks per group)
> =========
> case            	load    	baseline(std%)	compare%( std%)
> process-pipe    	group-1 	 1.00 (  4.51)	 +1.36 (  4.26)
> process-pipe    	group-2 	 1.00 ( 18.73)	 -9.66 ( 31.15)
> process-pipe    	group-3 	 1.00 ( 23.67)	 +8.52 ( 21.13)
> process-pipe    	group-4 	 1.00 ( 14.65)	+17.12 ( 25.23)
> process-pipe    	group-8 	 1.00 (  3.11)	+16.41 (  5.94)
> process-sockets 	group-1 	 1.00 (  8.83)	 +1.53 ( 11.93)
> process-sockets 	group-2 	 1.00 (  5.32)	-15.43 (  7.17)
> process-sockets 	group-3 	 1.00 (  4.79)	 -4.14 (  1.90)
> process-sockets 	group-4 	 1.00 (  2.39)	 +4.37 (  1.31)
> process-sockets 	group-8 	 1.00 (  0.38)	 +4.41 (  0.05)
> threads-pipe    	group-1 	 1.00 (  3.06)	 -1.57 (  3.71)
> threads-pipe    	group-2 	 1.00 ( 17.41)	 -2.16 ( 15.29)
> threads-pipe    	group-3 	 1.00 ( 17.94)	+19.86 ( 13.24)
> threads-pipe    	group-4 	 1.00 ( 15.38)	 +3.71 ( 11.97)
> threads-pipe    	group-8 	 1.00 (  2.72)	+13.40 (  8.43)
> threads-sockets 	group-1 	 1.00 (  8.51)	 -2.73 ( 17.48)
> threads-sockets 	group-2 	 1.00 (  5.44)	-12.04 (  5.91)
> threads-sockets 	group-3 	 1.00 (  4.38)	 -5.00 (  1.48)
> threads-sockets 	group-4 	 1.00 (  1.08)	 +4.46 (  1.15)
> threads-sockets 	group-8 	 1.00 (  0.61)	 +5.12 (  0.20)
> 
> netperf
> =======
> case            	load    	baseline(std%)	compare%( std%)
> TCP_RR          	thread-48	 1.00 (  3.79)	 +4.69 (  4.03)
> TCP_RR          	thread-96	 1.00 (  4.98)	 -6.74 (  3.59)
> TCP_RR          	thread-144	 1.00 (  6.04)	 -2.36 (  3.57)
> TCP_RR          	thread-192	 1.00 (  4.97)	 -0.44 (  4.89)
> TCP_RR          	thread-384	 1.00 ( 19.87)	-19.12 ( 28.99)
> UDP_RR          	thread-48	 1.00 ( 12.54)	 -2.73 (  1.59)
> UDP_RR          	thread-96	 1.00 (  6.51)	 -6.66 ( 10.42)
> UDP_RR          	thread-144	 1.00 ( 45.41)	 -3.81 ( 31.37)
> UDP_RR          	thread-192	 1.00 ( 32.06)	 +3.07 ( 71.89)
> UDP_RR          	thread-384	 1.00 ( 29.57)	-21.52 ( 35.50)

-- 
Thanks and Regards
Srikar Dronamraju