Re: [PATCH] barrier patch set
From: Jeff Garzik (jgarzik_at_pobox.com)
Date: 03/31/04
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Date: Wed, 31 Mar 2004 16:27:32 -0500 To: "Stephen C. Tweedie" <sct@redhat.com>
Stephen C. Tweedie wrote:
> Hi,
>
> On Tue, 2004-03-30 at 23:21, Jeff Garzik wrote:
>
>
>>For IDE, O_DIRECT and O_SYNC can use special "FUA" commands, which don't
>>return until the data is on the platter.
>
>
> fsync() is still really nasty, because that can require that we wait on
> IO that was submitted by the VM before we knew that there was a
> synchronous IO wait coming. SCSI also has an FUA bit that can make a
> difference if you've got writeback caching enabled. (And FUA on read
> can bypass drive writethrough caches, too, for media verification.)
Agreed, but I did not mention fsync(), since that would not be
appropriate to FUA like O_DIRECT or O_SYNC might be.
Jeff
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