From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Woodhouse Subject: Re: [PATCH 1/7] Make DISCARD_BARRIER and DISCARD_NOBARRIER writes instead of reads Date: Thu, 03 Sep 2009 18:52:20 +0100 Message-ID: <1252000340.4483.529.camel@macbook.infradead.org> References: <20090829230332.017137693@bombadil.infradead.org> <20090829231121.144124147@bombadil.infradead.org> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20090829231121.144124147@bombadil.infradead.org> Sender: linux-ide-owner@vger.kernel.org To: Christoph Hellwig Cc: linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org, liml@rtr.ca, jens.axboe@oracle.com, matthew@wil.cx, Matthew Wilcox List-Id: linux-scsi@vger.kernel.org On Sat, 2009-08-29 at 19:03 -0400, Christoph Hellwig wrote: > > The commands are conceptually writes, and in the case of IDE and SCSI > commands actually are writes. They were only reads because we thought > that would interact better with the elevators. Now the elevators know > about discard requests, that advantage no longer exists. Can you drop the final sentence of that? It isn't true, and I never said it. s/. Now.*/, but that isn't necessary, and making them writes makes it easier for the low-level IDE and SCSI code to cope with the fact that the command has to be sent with a payload./ The elevators _still_ don't know about discards, and will still let reads and writes (and discards, which are just a special case of writes) to the same sector all cross each other on the queue unless there's some external factor to prevent it. -- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation