From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: libata: clustering on or off? Date: Sun, 28 Aug 2005 16:20:19 +0200 Message-ID: <20050828142018.GS4018@suse.de> References: <20050828094218.GA29145@havoc.gtf.org> <1125224541.3219.13.camel@laptopd505.fenrus.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from ns.virtualhost.dk ([195.184.98.160]:15233 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S1751171AbVH1OUW (ORCPT ); Sun, 28 Aug 2005 10:20:22 -0400 Content-Disposition: inline In-Reply-To: <1125224541.3219.13.camel@laptopd505.fenrus.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Arjan van de Ven Cc: Jeff Garzik , linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org On Sun, Aug 28 2005, Arjan van de Ven wrote: > On Sun, 2005-08-28 at 05:42 -0400, Jeff Garzik wrote: > > The constant ATA_SHT_USE_CLUSTERING in include/linux/libata.h controls > > the use of SCSI layer's use_clustering feature, for a great many libata > > drivers. > > > > The current setup has clustering disabled, which in theory causes the > > block layer to do less work, at the expense of a greater number of > > scatter/gather table entries used. > > > > Any opinions WRT turning on clustering for libata? > > in 2.4 clustering was expensive due to a large number of checks that > were done (basically the number of fragments got recounted a gazilion > times). In 2.6 Jens fixed that afaik to make it basically free... > at which point it's a win always. Yeah, it wont cost any extra cycles, so there's no point in keeping it turned off for that reason. > Imo clustering on the driver level should announce driver capabilities. > If clustering for some arch/kernel makes it slower, that should be > decided at a midlayer level and not in each driver; eg the midlayer > would chose to ignore the drivers capabilities. > So .. my opinion would be that libata should announce the capability (it > seems the code/hw can do it). Agree, we should just remove the ability to control clustering, as it really overlaps with the segment settings anyways. -- Jens Axboe