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From: Jens Axboe <jens.axboe@oracle.com>
To: Tejun Heo <htejun@gmail.com>
Cc: Robert Hancock <hancockr@shaw.ca>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	linux-ide@vger.kernel.org, edmudama@gmail.com,
	Nicolas.Mailhot@LaPoste.net, Jeff Garzik <jeff@garzik.org>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>, Mark Lord <mlord@pobox.com>,
	Ric Wheeler <ric@emc.com>, Dongjun Shin <d.j.shin@samsung.com>,
	Hannes Reinecke <hare@suse.de>
Subject: Re: libata FUA revisited
Date: Wed, 21 Feb 2007 09:46:13 +0100	[thread overview]
Message-ID: <20070221084613.GB3924@kernel.dk> (raw)
In-Reply-To: <45DC04DF.8040002@gmail.com>

On Wed, Feb 21 2007, Tejun Heo wrote:
> [cc'ing Ric, Hannes and Dongjun, Hello.  Feel free to drag other people in.]
> 
> Robert Hancock wrote:
> > Jens Axboe wrote:
> >> But we can't really change that, since you need the cache flushed before
> >> issuing the FUA write. I've been advocating for an ordered bit for
> >> years, so that we could just do:
> >>
> >> 3. w/FUA+ORDERED
> >>
> >> normal operation -> barrier issued -> write barrier FUA+ORDERED
> >>  -> normal operation resumes
> >>
> >> So we don't have to serialize everything both at the block and device
> >> level. I would have made FUA imply this already, but apparently it's not
> >> what MS wanted FUA for, so... The current implementations take the FUA
> >> bit (or WRITE FUA) as a hint to boost it to head of queue, so you are
> >> almost certainly going to jump ahead of already queued writes. Which we
> >> of course really do not.
> 
> Yeah, I think if we have tagged write command and flush tagged (or
> barrier tagged) things can be pretty efficient.  Again, I'm much more
> comfortable with separate opcodes for those rather than bits changing
> the behavior.

ORDERED+FUA NCQ would still be preferable to an NCQ enabled flush
command, though.

> Another idea Dongjun talked about while drinking in LSF was ranged
> flush.  Not as flexible/efficient as the previous option but much less
> intrusive and should help quite a bit, I think.

But that requires extensive tracking, I'm not so sure the implementation
of that for barriers would be very clean. It'd probably be good for
fsync, though.

-- 
Jens Axboe


  reply	other threads:[~2007-02-21  8:46 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <fa.S80SRyQbD/hm4SxliPUKU88BaCo@ifi.uio.no>
2007-02-12  5:47 ` Robert Hancock
     [not found] ` <fa.Q/csgyCHkAsD84yi+bN78H1WNNM@ifi.uio.no>
2007-02-13  0:23   ` Robert Hancock
2007-02-13 15:20     ` Tejun Heo
2007-02-14  0:07       ` Robert Hancock
2007-02-14  0:50         ` Tejun Heo
2007-02-15 18:00           ` Jens Axboe
2007-02-19 19:46             ` Robert Hancock
2007-02-21  8:37               ` Tejun Heo
2007-02-21  8:46                 ` Jens Axboe [this message]
2007-02-21  8:57                   ` Tejun Heo
2007-02-21  9:01                     ` Jens Axboe
2007-02-22 22:44                     ` Ric Wheeler
2007-02-22 22:40                   ` Ric Wheeler
2007-02-21 14:06                 ` Robert Hancock
2007-02-22 22:34                 ` Ric Wheeler
2007-02-23  0:04                   ` Robert Hancock
2007-02-21  8:44               ` Jens Axboe
2007-02-12  3:25 Robert Hancock
2007-02-12  8:31 ` Tejun Heo
2007-02-16 18:14   ` Jeff Garzik

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