Re: BFQ speed tests [was Re: [PATCH RFC - TAKE TWO - 00/12] New version of the BFQ I/O Scheduler]

[Takashi Iwai <tiwai@suse.de>]

At Wed, 11 Jun 2014 22:45:06 +0200,
Paolo Valente wrote:
> 
> 
> Il giorno 04/giu/2014, alle ore 13:59, Takashi Iwai <tiwai@suse.de> ha scritto:
> 
> > […]
> > I've been using BFQ for a while and noticed also some obvious
> > regression in some operations, notably git, too.
> > For example, git grep regresses badly.
> > 
> > I ran "test git grep foo > /dev/null" on linux kernel repos on both
> > rotational disk and SSD.
> > […]
> > 
> > BFQ seems behaving bad when reading many small files.
> > 
> 
> The fix I described in my last reply to Pavel's speed tests
> (https://lkml.org/lkml/2014/6/4/94) apparently solves also this problem.
> As I wrote in that reply, the new fixed version of bfq is here:
> http://algogroup.unimore.it/people/paolo/disk_sched/debugging-patches/3.16.0-rc0-v7rc5.tgz
> 
> These are our results, for your test, with this fixed version of bfq.
> 
> time git grep foo > /dev/null
> 
> Rotational disk:
>  CFQ:
>    2.86user 4.87system 0:29.51elapsed 26%CPU
>    2.87user 4.87system 0:30.30elapsed 25%CPU
>    2.82user 4.90system 0:29.13elapsed 26%CPU
> 
>  BFQ:
>    2.81user 4.97system 0:25.96elapsed 29%CPU
>    2.83user 5.02system 0:24.79elapsed 31%CPU
>    2.85user 4.95system 0:24.73elapsed 31%CPU
> 
> SSD:
>  CFQ:
>    2.04user 3.93system 0:03.88elapsed 153%CPU
>    2.12user 3.85system 0:03.89elapsed 153%CPU
>    2.05user 3.92system 0:03.89elapsed 153%CPU
> 
>  BFQ:
>    2.10user 3.86system 0:03.89elapsed 153%CPU
>    2.05user 3.90system 0:03.88elapsed 153%CPU
>    2.01user 3.95system 0:03.89elapsed 153%CPU
> 
> time git grep foo HEAD > /dev/null
> 
> SSD:
>  CFQ:
>    5.11user 0.38system 0:06.71elapsed 81%CPU
>    5.21user 0.36system 0:06.78elapsed 82%CPU
>    5.05user 0.41system 0:06.69elapsed 81%CPU
> 
>  BFQ:
>    5.17user 0.39system 0:06.77elapsed 82%CPU
>    5.13user 0.37system 0:06.73elapsed 81%CPU
>    5.17user 0.37system 0:06.78elapsed 81%CPU
> 
> Should you be willing to provide further feedback on this and other tests,
> we would of course really appreciate it.

Thanks.  The new patchset works well now.  The results with the new
patchset + latest Linus git tree are below.

The only significant difference is the case with "git grep foo" on
SSD.  But I'm not sure whether it's a casual error.  I'll need to get
more samples to flatten the errors.


Takashi

===

* time git grep foo > /dev/null

rotational disk:
  CFQ:
    2.34user 4.04system 2:00.12elapsed 5%CPU
    2.49user 3.80system 1:56.20elapsed 5%CPU
    2.42user 3.68system 1:46.81elapsed 5%CPU

  BFQ:
    2.44user 3.57system 1:49.65elapsed 5%CPU
    2.47user 3.67system 1:55.92elapsed 5%CPU
    2.47user 3.63system 1:50.06elapsed 5%CPU

SSD:
  CFQ:
    1.25user 1.54system 0:04.62elapsed 60%CPU
    1.23user 1.67system 0:04.65elapsed 62%CPU
    1.22user 1.60system 0:04.61elapsed 61%CPU

  BFQ:
    1.29user 1.64system 0:06.91elapsed 42%CPU
    1.30user 1.66system 0:06.66elapsed 44%CPU
    1.27user 1.59system 0:04.73elapsed 60%CPU

* time git grep foo HEAD > /dev/null

rotational disk:
  CFQ:
    5.12user 0.43system 0:19.86elapsed 28%CPU
    5.06user 0.45system 0:19.88elapsed 27%CPU
    5.00user 0.41system 0:20.05elapsed 27%CPU

  BFQ:
    4.82user 0.37system 0:19.56elapsed 26%CPU
    5.00user 0.43system 0:19.53elapsed 27%CPU
    4.92user 0.45system 0:19.69elapsed 27%CPU

SSD:
  CFQ:
    4.49user 0.32system 0:07.26elapsed 66%CPU
    4.50user 0.31system 0:07.25elapsed 66%CPU
    4.40user 0.32system 0:07.16elapsed 65%CPU

  BFQ:
    4.09user 0.26system 0:06.93elapsed 62%CPU
    3.76user 0.23system 0:06.54elapsed 61%CPU
    3.65user 0.22system 0:06.40elapsed 60%CPU