From: Dmitry Monakhov <dmonakhov@openvz.org>
To: Jan Kara <jack@suse.cz>
Cc: ext4 development <linux-ext4@vger.kernel.org>, Jan Kara <jack@suse.cz>
Subject: Re: per inode fsync optimization question
Date: Wed, 03 Apr 2013 19:09:33 +0400 [thread overview]
Message-ID: <87zjxfps5u.fsf@openvz.org> (raw)
In-Reply-To: <20130403145055.GD14667@quack.suse.cz>
On Wed, 3 Apr 2013 16:50:55 +0200, Jan Kara <jack@suse.cz> wrote:
> On Wed 03-04-13 18:21:46, Dmitry Monakhov wrote:
> > inode store i_sync_tid and i_datasync_tid in order to optimize journal
> > flushes and wait for commits only when necessary, but
> > fields are declared as tid_t(not atomic_t as it done in ext3) so we
> > have not synchronization between readers and writers, so gcc and cpu
> > is allowed to perform prefetch, cache and other stuff.
> > Looks like a bug, right?
> Reads and writes to atomic_t aren't guaranteed to be any kind of a
> barrier (if fact they are compiled as simple stores and loads on x86). Only
> arithmetic operations on atomic types are special. So using tid_t is just
> fine.
Ok but what about prefetching?
Compiler is allowed to prefetch on early stage ?
should we use ACCESS_ONCE() or wmb() and rmb() here?
>
> Honza
> --
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
next prev parent reply other threads:[~2013-04-03 15:09 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-03 14:21 per inode fsync optimization question Dmitry Monakhov
2013-04-03 14:50 ` Jan Kara
2013-04-03 15:09 ` Dmitry Monakhov [this message]
2013-04-03 15:15 ` Jan Kara
2013-04-03 15:41 ` Dmitry Monakhov
2013-04-03 16:03 ` Jan Kara
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