From: Jens Axboe <axboe@kernel.dk>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: fio@vger.kernel.org, Asias He <asias@redhat.com>
Subject: Re: Why does 'direct' influence 'fsync'?
Date: Sat, 26 Jan 2013 18:37:12 -0700 [thread overview]
Message-ID: <20130127013712.GJ15635@kernel.dk> (raw)
In-Reply-To: <CAJSP0QURHyhFGc3ZVo=TM16_VUY-pRqNMTOJcNwNGUoJCdoi0Q@mail.gmail.com>
On Sat, Jan 26 2013, Stefan Hajnoczi wrote:
> On Sat, Jan 26, 2013 at 5:28 PM, Jens Axboe <axboe@kernel.dk> wrote:
> > On Fri, Jan 25 2013, Stefan Hajnoczi wrote:
> >> Is there a way to flush the disk write cache when O_DIRECT is in use?
> >>
> >> It seems that direct=1 causes the fsync setting to be ignored. Asias
> >> writes:
> >>
> >> > The O_DIRECT do affect the flush behaviour. e.g
> >> >
> >> > guest$ fio --fsync=100 --direct=1
> >> > No virtio_blk_handle_flush is observed on host side every 100 IOs
> >> >
> >> > guest$ fio --fsync=100 --direct=0
> >> > virtio_blk_handle_flush is observed on host side every 100 IOs
> >>
> >> Am I missing a reason for this behavior? To me it seems weird since you
> >> could already use --fsync=0 --direct=1 if you want to guarantee that
> >> fsync is not called. I don't see a need to override the fsync setting.
> >
> > You are right, fio should not be double guessing options like that. If
> > you ask for fsync, you should get fsync.
> >
> > Does the below work for you?
>
> Yes, thanks!
>
> Tested-by: Stefan Hajnoczi <stefanha@redhat.com>
Great, thanks for reporting and testing!
--
Jens Axboe
prev parent reply other threads:[~2013-01-27 1:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-25 11:42 Why does 'direct' influence 'fsync'? Stefan Hajnoczi
2013-01-26 16:28 ` Jens Axboe
2013-01-26 16:51 ` Stefan Hajnoczi
2013-01-27 1:37 ` Jens Axboe [this message]
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