Re: yum upgrade on btrfs very slow

Tomasz Torcz
2009-09-30T19:43:51Z

On Tue, Sep 29, 2009 at 09:25:38AM -0400, Chris Mason wrote:
> On Tue, Sep 29, 2009 at 08:18:22AM +0200, Tomasz Torcz wrote:
> > On Mon, Sep 28, 2009 at 09:35:43AM -0400, Chris Mason wrote:
> > > > Every yum activity is very slow, like 15 minutes for installation of 11
> > > > packages 25MB in size. Kernel is 2.6.31.1-48.fc12.x86_64, btrfs-progs-0.19-7.fc12.x86_64.
> > > > Hardware is pentium 4 3.0 GHz (Hyperthreading, 64 bit), with single IDE disk
> > > > on Intel ICH controller.
> > >
> > > You're doing quite a lot of reads, and some writes. Could you please
> > > capture the output of sysrq-w at 5s intervals during the upgrade?
> >
> > It got quite big (over 100 KiB, over 1 MiB after unpacking), so I
> > put it at http://pipebreaker.pl/dump/sysrq-w_every_5_sec.txt.bz2
>
> Ok, you've got 158 sysrq-w runs in here, and 119 of them involve fsync.
> This is good because it is what Josef expected the problem to be.
>
> The first thing I would try is mount -o ssd. I think what is happening
> is that we are seeking around while fsyncing files. mount -o ssd isn't
> really the right long term answer but it will tell us if I've got it
> right.

Tried that. Not noticable faster. Dumps are here:
http://pipebreaker.pl/dump/sysrq_w-with_ssd.txt.bz2
http://pipebreaker.pl/dump/vmstat-with.ssd.txt.bz2

>
> If you're comparing w/ext3 and wondering why btrfs is sooooooo much
> slower it might be because btrfs has barriers on by default and ext3
> doesn't. You could mount -o nobarrier for btrfs or mount -o barrier=1
> for ext3 for a proper comparison.
>
> (Assuming your dmesg doesn't have messages from btrfs about disabling
> barriers).

I wouldn't expect barriers to work here (reminder, this is PATA drive
on ICH7 sata controller), but I will test tomorrow with nobarrier.
Then I probably check his "yum upgrade" under seekwatcher on friday.

--
Tomasz Torcz Morality must always be based on practicality.
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