Message-ID: <1429823050.26534.9.camel@redhat.com>
Subject: loop block-mq conversion scalability issues
From: "Justin M. Forbes" <jforbes@redhat.com>
To: ming.lei@canonical.com
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Date: Thu, 23 Apr 2015 16:04:10 -0500
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The block-mq conversion for loop in 4.0 kernels is showing us an
interesting scalability problem with live CDs (ro, squashfs).  It was
noticed when testing the Fedora beta that the more CPUs a liveCD image
was given, the slower it would boot. A 4 core qemu instance or bare
metal instance took more than twice as long to boot compared to a single
CPU instance.  After investigating, this came directly to the block-mq
conversion, reverting these 4 patches will return performance. More
details are available at
https://bugzilla.redhat.com/show_bug.cgi?id=1210857
I don't think that reverting the patches is the ideal solution so I am
looking for other options.  Since you know this code a bit better than I
do I thought I would run it by you while I am looking as well.

Thanks,
Justin

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