linux-kernel - Re: [RESEND] [PATCH] readahead:add blk_run_backing

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Date:	Tue, 28 Jul 2009 11:51:00 +0200
From:	Ronald Moesbergen <intercommit@...il.com>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	fengguang.wu@...el.com, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	Alan.Brunelle@...com, linux-fsdevel@...r.kernel.org,
	jens.axboe@...cle.com, randy.dunlap@...cle.com,
	Bart Van Assche <bart.vanassche@...il.com>
Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev

2009/7/27 Vladislav Bolkhovitin <vst@...b.net>:
>
> Hmm, it's really weird, why the case of 2 threads is faster. There must be
> some commands reordering somewhere in SCST, which I'm missing, like
> list_add() instead of list_add_tail().
>
> Can you apply the attached patch and repeat tests 5, 8 and 11 with 1 and 2
> threads, please. The patch will enable forced commands order protection,
> i.e. with it all the commands will be executed in exactly the same order as
> they were received.

The patched source doesn't compile. I changed the code to this:

@ line 3184:

        case SCST_CMD_QUEUE_UNTAGGED:
#if 1 /* left for future performance investigations */
                goto ordered;
#endif

The results:

Overall performance seems lower.

client kernel: 2.6.26-15lenny3 (debian)
server kernel: 2.6.29.5 with readahead-context, blk_run_backing_dev
and io_context, forced_order

With one IO thread:
5) client: default, server: default (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  16.484   16.417   16.068   62.741    0.706    0.980
 33554432  15.684   16.348   16.011   63.961    1.083    1.999
 16777216  16.044   16.239   15.938   63.710    0.493    3.982

8) client: default, server: 64 max_sectors_kb, RA 2MB (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  16.127   15.784   16.210   63.847    0.740    0.998
 33554432  16.103   16.072   16.106   63.627    0.061    1.988
 16777216  16.637   16.058   16.154   62.902    0.970    3.931

11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA 2MB (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  13.417   15.219   13.912   72.405    3.785    1.131
 33554432  13.868   13.789   14.110   73.558    0.718    2.299
 16777216  13.691   13.784   10.280   82.898   11.822    5.181

11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA
2MB (deadline)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  13.604   13.532   13.978   74.733    1.055    1.168
 33554432  13.523   13.166   13.504   76.443    0.945    2.389
 16777216  13.434   13.409   13.632   75.902    0.557    4.744

With two threads:
5) client: default, server: default (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  16.206   16.001   15.908   63.851    0.493    0.998
 33554432  16.927   16.033   15.991   62.799    1.631    1.962
 16777216  16.566   15.968   16.212   63.035    0.950    3.940

8) client: default, server: 64 max_sectors_kb, RA 2MB (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  16.017   15.849   15.748   64.521    0.450    1.008
 33554432  16.652   15.542   16.259   63.454    1.823    1.983
 16777216  16.456   16.071   15.943   63.392    0.849    3.962

11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA 2MB (cfq)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  14.109    9.985   13.548   83.572   13.478    1.306
 33554432  13.698   14.236   13.754   73.711    1.267    2.303
 16777216  13.610   12.090   14.136   77.458    5.244    4.841

11) client: 64 max_sectors_kb, 2MB. RA server: 64 max_sectors_kb, RA
2MB (deadline)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  13.542   13.975   13.978   74.049    1.110    1.157
 33554432   9.921   13.272   13.321   85.746   12.349    2.680
 16777216  13.850   13.600   13.344   75.324    1.144    4.708

Ronald.
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