From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: libata: set queue SSD flag for SSD devices Date: Sat, 11 Oct 2008 16:06:01 +0200 Message-ID: <20081011140600.GR19428@kernel.dk> References: <200810101904.m9AJ42Gq018897@hera.kernel.org> <20081010202515.446857cc@lxorguk.ukuu.org.uk> <20081010200528.GJ19428@kernel.dk> <20081010175508.3d1ed2a4@infradead.org> <1223710417.4159.11.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from pasmtpa.tele.dk ([80.160.77.114]:38495 "EHLO pasmtpA.tele.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753059AbYJKOGh (ORCPT ); Sat, 11 Oct 2008 10:06:37 -0400 Content-Disposition: inline In-Reply-To: <1223710417.4159.11.camel@localhost.localdomain> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: James Bottomley Cc: Arjan van de Ven , Alan Cox , Linux Kernel Mailing List , linux-ide@vger.kernel.org, torvalds@osdl.org On Sat, Oct 11 2008, James Bottomley wrote: > On Fri, 2008-10-10 at 17:55 -0700, Arjan van de Ven wrote: > > On Fri, 10 Oct 2008 22:05:28 +0200 > > Jens Axboe wrote: > > > > > > In this specific patch, it'll do no harm at least since I very much > > > doubt we'll see a false positive. And even if, the consequences wont > > > be dire. But it does want the version check, of course. > > > > > > > also, is "is an ssd" the right question or is "doesn't have seek > > latency" the right one? > > (difference is.. well EMC boxes with lots of ram etc) > > For libata, the is ssd is the right test. > > For things like the symmetrix we probably need to look at the caching > mode page and treat it like ssd if the cache is say > 1GB or whatever > heuristic is needed. Still wont quite work, you're still going to have occasional seek latencies no matter how large the cache is (unless it's == device size :-) So we need something a bit more involved, but not too complex. A fine line... -- Jens Axboe