From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ronald Moesbergen <intercommit@gmail.com>
Subject: Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev
Date: Mon, 3 Aug 2009 11:15:32 +0200
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Cc: fengguang.wu@intel.com, linux-kernel@vger.kernel.org,
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To: Vladislav Bolkhovitin <vst@vlnb.net>
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2009/7/31 Vladislav Bolkhovitin <vst@vlnb.net>:
>
> OK, as I expected, on the SCST level everything is clear and the forced
> ordering change didn't change anything.
>
> But still, a single read stream must be the fastest from single thread.
> Otherwise, there's something wrong somewhere in the I/O path: block layer,
> RA, I/O scheduler. And, apparently, this is what we have and should find out
> the cause.
>
> Can you check if noop on the target and/or initiator makes any difference?
> Case 5 with 1 and 2 threads will be sufficient.

That doesn't seem to help:

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 (server noop, client noop)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  17.612   21.113   21.355   51.532    4.680    0.805
 33554432  18.329   18.523   19.049   54.969    0.891    1.718
 16777216  18.497   18.219   17.042   57.217    2.059    3.576

With two threads:
5) client: default, server: default (server noop, client noop)
blocksize       R        R        R   R(avg,    R(std        R
  (bytes)     (s)      (s)      (s)    MB/s)   ,MB/s)   (IOPS)
 67108864  17.436   18.376   20.493   54.807    3.634    0.856
 33554432  17.466   16.980   18.261   58.337    1.740    1.823
 16777216  18.222   17.567   18.077   57.045    0.901    3.565

Ronald.