linux-kernel - Re: balance storm

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Message-ID: <1401090987.5339.79.camel@marge.simpson.net>
Date:	Mon, 26 May 2014 09:56:27 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Libo Chen <libo.chen@...wei.com>
Cc:	tglx@...utronix.de, mingo@...e.hu,
	LKML <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>,
	Li Zefan <lizefan@...wei.com>
Subject: Re: balance storm

On Mon, 2014-05-26 at 11:04 +0800, Libo Chen wrote: 
> hi,
>     my box has 16 cpu (E5-2658,8 core, 2 thread per core), i did a test on
> 3.4.24stable, startup 50 same process, every process is sample:
> 
>  	#include <unistd.h>
> 
>  	int main()
>  	{
>           	for (;;)
>           	{
>                   	unsigned int i = 0;
>                  	 while (i< 100){
>                      	 i++;
>                   	}
>                   	usleep(100);
>           	}
> 
>          	 return 0;
>   	}
> 
> the result is process uses 15% cpu time, perf tool shows 70w migrations in 5 second.

My 8 socket 64 core DL980 running 256 copies (3.14-rt5) munches ~4%/copy
per top, and does roughly 1 sh*tload migrations, nano-work loop or not.
Turn SD_SHARE_PKG_RESOURCES off at MC (not a noop here), and consumption
drops to ~2%/copy, and migrations ('course) mostly go away.

vogelweide:/abuild/mike/:[0]# perf stat -a -e sched:sched_migrate_task -- sleep 5

 Performance counter stats for 'system wide':

              3108      sched:sched_migrate_task                                    

       5.001367910 seconds time elapsed

(turns SD_SHARE_PKG_RESOURCES back on)

vogelweide:/abuild/mike/:[0]# perf stat -a -e sched:sched_migrate_task -- sleep 5

 Performance counter stats for 'system wide':

           4182334      sched:sched_migrate_task                                    

       5.001365023 seconds time elapsed

vogelweide:/abuild/mike/:[0]# 

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