linux-kernel - Re: [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock waiter

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Message-ID: <56F0B9A6.4040903@hpe.com>
Date:	Mon, 21 Mar 2016 23:19:02 -0400
From:	Waiman Long <waiman.long@....com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ding Tianhong <dingtianhong@...wei.com>,
	Jason Low <jason.low2@....com>,
	Davidlohr Bueso <dave@...olabs.net>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <Will.Deacon@....com>,
	Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH v2 0/4] locking/mutex: Enable optimistic spinning of lock
 waiter

On 02/16/2016 03:51 AM, Peter Zijlstra wrote:
> On Fri, Feb 12, 2016 at 12:32:11PM -0500, Waiman Long wrote:
>> My own test on a 4-socket E7-4820 v3 system showed a regression of
>> about 4% in the high_systime workload with Peter's patch which this
>> new patch effectively eliminates.
>>
>> Testing on an 8-socket Westmere-EX server, however, has performance
>> change from -9% to than +140% on the fserver workload of AIM7
>> depending on how the system was set up.
> Subject: [lkp] [locking/mutex] aaca135480: -72.9% fsmark.files_per_sec
>
> My patch also generated the above email.
>
> Please also test that benchmark against this approach.
>

I also got an email from "kernel test robot", it didn't list fsmark at 
all. Instead, the subject was

[lkp] [locking/mutex] 5267438002: +38.9% 
fileio.time.involuntary_context_switches

       4409 ±  1%     +38.9%       6126 ±  2%  
fileio.time.involuntary_context_switches
       6.00 ±  0%     +33.3%       8.00 ±  0%  
fileio.time.percent_of_cpu_this_job_got
      36.06 ±  0%     +43.0%      51.55 ±  0%  fileio.time.system_time
    1828660 ±  0%     -92.5%     137258 ±  0%  
fileio.time.voluntary_context_switches

Given that the number of voluntary context switches dropped by 92.5%, an 
increase in involuntary context switches that is order of magnitude less 
than the voluntary context switches should be OK, I think.

Do you know how to report back that this increase is expected and is 
nothing to worry about? Do I just reply it back?

Cheers,
Longman