From: Thanos Makatos <mcatos@ics.forth.gr>
To: linux-kernel@vger.kernel.org
Subject: Inexplicable I/O latency using worker threads
Date: Fri, 12 Dec 2008 11:39:26 +0200 [thread overview]
Message-ID: <4942314E.80408@ics.forth.gr> (raw)
Hello all.
I am facing a weird problem with a virtual block driver I made concerning excessive I/O latency.
My block driver intercepts requests and redirects them to a real block device,
but not just be setting the bio->bi_bdev field, I create new bios.
Anyway, my problem is that for load balancing reasons I need per-CPU worker threads
where I enqueue requests and let them do all the work. If I use 2 threads in a round
robin manner (request 1 served by CPU 0, 2 by CPU1, 3 by CPU0 and so on), performance
is inexplicably low.
If I choose only one CPU to act as a worker the problem is gone. The difference of measured
I/O latency is more than 30 times.
What could be happening?
I'm using a vanilla 2.6.18.8.
Thanx in advance.
next reply other threads:[~2008-12-12 11:22 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-12-12 9:39 Thanos Makatos [this message]
2008-12-12 17:46 ` Inexplicable I/O latency using worker threads Chris Snook
2008-12-13 12:44 ` Thanos McAtos
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