From: Michael Tokarev <mjt@tls.msk.ru>
To: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>,
Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: dramatic I/O slowdown after upgrading 2.6.38->3.0+
Date: Tue, 10 Apr 2012 10:00:38 +0400 [thread overview]
Message-ID: <4F83CC86.2010805@msgid.tls.msk.ru> (raw)
In-Reply-To: <20120410022628.GN18323@dastard>
On 10.04.2012 06:26, Dave Chinner wrote:
> Barriers. Turn them off, and see if that fixes your problem.
Thank you Dave for a hint. And nope, that's not it, not at all... ;)
While turning off barriers helps a tiny bit, to gain a few %% from
the huge slowdown, it does not cure the issue.
Meanwhile, I observed the following:
1) the issue persists on more recent kernels too, I tried 3.3
and it is also as slow as 3.0.
2) at least 2.6.38 kernel works fine, as fast as 2.6.32, I'll
try 2.6.39 next.
I updated $subject accordingly.
3) the most important thing I think: this is general I/O speed
issue. Here's why:
2.6.38:
# dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 1.73126 s, 60.6 MB/s
3.0:
# dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 29.4508 s, 3.6 MB/s
That's about 20 times difference on direct read from the
same - idle - device!!
Preparing for another bisect attempt, slowly.....
Thank you!
/mjt
next prev parent reply other threads:[~2012-04-10 6:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-30 16:50 dramatic I/O slowdown after upgrading 2.6.32->3.0 Michael Tokarev
2012-04-02 16:58 ` Jonathan Corbet
2012-04-05 23:29 ` Jan Kara
2012-04-06 4:45 ` Michael Tokarev
2012-04-10 2:26 ` Dave Chinner
2012-04-10 6:00 ` Michael Tokarev [this message]
2012-04-10 15:13 ` dramatic I/O slowdown after upgrading 2.6.38->3.0+ Jan Kara
2012-04-10 19:25 ` Suresh Jayaraman
2012-04-10 19:51 ` Jan Kara
2012-04-11 0:20 ` Henrique de Moraes Holschuh
2012-04-11 9:40 ` Michael Tokarev
2012-04-11 17:19 ` Mike Christie
2012-04-11 17:55 ` Michael Tokarev
2012-04-11 18:28 ` Jan Kara
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