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Performance impact of CONFIG_DEBUG? direct-io test case

To: linux-kernel@xxxxxxxxxxxxxxx, mingo@xxxxxxxxxx, peterz@xxxxxxxxxxxxx
Subject: Performance impact of CONFIG_DEBUG? direct-io test case
From: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 5 Aug 2010 22:47:49 +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_DEBUG? 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, I get the following results:

1) best results are ~ 28 MB/s

2) Enabling CONFIG_DEBUG_LOCK_ALLOC, which also means CONFIG_LOCKDEP
   being enabled, causes the transfer rate to decrease by ~ 1.2 MB/s

3) Enabling CONFIG_DEBUG_SPINLOCK && CONFIG_DEBUG_MUTEXTES or
   CONFIG_DEBUG_SPINLOCK_SLEEP=y costs about ~ 0.4 MB/s each

4) Enabling all of the following options:
        CONFIG_DEBUG_RT_MUTEXES
        CONFIG_DEBUG_PI_LIST
        CONFIG_PROVE_LOCKING
        CONFIG_LOCK_STAT
        CONFIG_DEBUG_LOCKDEP
   costs another ~ 5 MB/s.

So, for this test case, the performance impact of (some) CONFIG_DEBUG
options is highly significant, here by about 25 %.

Best,
        Dominik

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