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Performance impact of CONFIG_SCHED_MC? direct-io test case

To: linux-kernel@xxxxxxxxxxxxxxx, mingo@xxxxxxxxxx, peterz@xxxxxxxxxxxxx
Subject: Performance impact of CONFIG_SCHED_MC? direct-io test case
From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 5 Aug 2010 22:54:48 +0200
Cc: Chris Mason <chris.mason@xxxxxxxxxx>, josef@xxxxxxxxxx, Valdis.Kletnieks@xxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx
In-reply-to: <20100805163519.GA6604@xxxxxxxxxxxxxxxxxxxxxxxxxx>
Mail-followup-to: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, mingo@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, Chris Mason <chris.mason@xxxxxxxxxx>, josef@xxxxxxxxxx, Valdis.Kletnieks@xxxxxx, Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-raid@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx
References: <20100805123649.GA18672@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100805113240.GA29846@think> <20100805153519.GA7242@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20100805163519.GA6604@xxxxxxxxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
How large is the performance impact of CONFIG_SCHED_MC -- for which there
is a warning that it comes "at a cost of slightly increased overhead in
some places."? Well, for the test workload I've been working with lately,

dd if=<device> of=/dev/zero bs=8k count=100000 iflag=direct

where <device> is a dm-crypted LVM volume consisting of several
partitions on a notebook pata harddisk, and all this runs on a Core2 Duo,
I get a ~ 10 % performance reduction if CONFIG_SCHED_MC is enabled.

Combined with the CONFIG_DEBUG performance reduction mentioned in the other
message, all of the reduction from 28 MB/s to 18 MB/s is explained for.

Best,
        Dominik

PS: Ingo: you got both mingo@xxxxxxx and mingo@xxxxxxxxxx in MAINTAINERS,
I suppose both are valid?

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