linux-kernel - Re: Linux 2.6.29

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Date:	Wed, 25 Mar 2009 21:22:50 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Ric Wheeler <rwheeler@...hat.com>
Cc:	Jeff Garzik <jeff@...zik.org>, Jens Axboe <jens.axboe@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Theodore Tso <tytso@....edu>, Ingo Molnar <mingo@...e.hu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>, David Rees <drees76@...il.com>,
	Jesper Krogh <jesper@...gh.cc>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 2.6.29

On Wed, 2009-03-25 at 16:25 -0400, Ric Wheeler wrote:
> Jeff Garzik wrote:
> > Ric Wheeler wrote:> And, as I am sure that you do know, to add insult 
> > to injury, FLUSH_CACHE
> >> is per device (not file system).
> >>
> >> When you issue an fsync() on a disk with multiple partitions, you 
> >> will flush the data for all of its partitions from the write cache....
> >
> > SCSI'S SYNCHRONIZE CACHE command already accepts an (LBA, length) 
> > pair.  We could make use of that.
> >
> > And I bet we could convince T13 to add FLUSH CACHE RANGE, if we could 
> > demonstrate clear benefit.
> >
> >     Jeff
> 
> How well supported is this in SCSI?  Can we try it out with a commodity 
> SAS drive?

What do you mean by well supported?  The way the SCSI standard is
written, a device can do a complete cache flush when a range flush is
requested and still be fully standards compliant.  There's no easy way
to tell if it does a complete cache flush every time other than by
taking the firmware apart (or asking the manufacturer).

James


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