From: Dave Chinner <david@fromorbit.com>
To: Premysl Kouril <premysl.kouril@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>, Andi Kleen <andi@firstfloor.org>,
linux-fsdevel@vger.kernel.org
Subject: Re: EXT4 vs LVM performance for VMs
Date: Tue, 16 Feb 2016 10:10:13 +1100 [thread overview]
Message-ID: <20160215231012.GV19486@dastard> (raw)
In-Reply-To: <CA+rfndJW=xXZKFh1Aag8DyCgW5b5Gz_XOOm0YsLP0nNnyui__w@mail.gmail.com>
On Mon, Feb 15, 2016 at 07:56:05PM +0100, Premysl Kouril wrote:
> Hello Dave,
>
> thanks for your suggestion. I've just recreated our tests with the XFS
> and preallocated raw files and the results seem almost same as with
> the EXT4. I again checked stuff with my Systemtap script and threads
> are waiting mostly waiting for locks in following placeS:
....
> Looking at this, does it suggest that the bottleneck is locking on the
> VFS layer? Or does my setup actually do DirectIO on the host level?
> You and Sanidhya mentioned that XFS is good at concurrent DirectIO as
> it doesn't hold lock on file, but I do see this in the trace:
>
> 0xffffffff8176fcaf : mutex_lock+0x1f/0x2f [kernel]
> 0xffffffffc073c531 : 0xffffffffc073c531 [xfs]
> 0xffffffffc07a788a : 0xffffffffc07a788a [xfs]
> 0xffffffffc073dd4c : 0xffffffffc073dd4c [xfs]
You need to resolve these addresses to symbols so we can see where
this is actually blocking.
> So either KVM is not doing directIO or there is some lock xfs must
> hold to do the write, right?
My guess is that you didn't configure KVM to use direct Io
correctly, because if it was XFs blocking on internal locks in
direct IO it would be on a rwsem, not a mutex.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
prev parent reply other threads:[~2016-02-15 23:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-11 20:50 EXT4 vs LVM performance for VMs Premysl Kouril
2016-02-12 6:12 ` Andi Kleen
2016-02-12 9:09 ` Premysl Kouril
2016-02-12 13:38 ` Theodore Ts'o
2016-02-12 14:13 ` Premysl Kouril
2016-02-12 16:53 ` Theodore Ts'o
2016-02-12 17:38 ` Premysl Kouril
2016-02-13 2:15 ` Dave Chinner
2016-02-13 21:56 ` Sanidhya Kashyap
2016-02-13 23:40 ` Jaegeuk Kim
2016-02-14 0:01 ` Dave Chinner
2016-02-15 18:56 ` Premysl Kouril
2016-02-15 19:11 ` Liu Bo
2016-02-15 23:10 ` Dave Chinner [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160215231012.GV19486@dastard \
--to=david@fromorbit.com \
--cc=andi@firstfloor.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=premysl.kouril@gmail.com \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.