From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bart Van Assche Subject: Re: SCSI mid layer and high IOPS capable devices Date: Thu, 13 Dec 2012 12:40:27 +0100 Message-ID: <50C9BEAB.6010702@acm.org> References: <20121211000013.GI23107@beardog.cce.hp.com> <50C6ED1A.7040404@acm.org> <20121211224626.GB20898@beardog.cce.hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from gerard.telenet-ops.be ([195.130.132.48]:60266 "EHLO gerard.telenet-ops.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750860Ab2LMLka (ORCPT ); Thu, 13 Dec 2012 06:40:30 -0500 In-Reply-To: <20121211224626.GB20898@beardog.cce.hp.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: scameron@beardog.cce.hp.com Cc: linux-scsi@vger.kernel.org, stephenmcameron@gmail.com, dab@hp.com On 12/11/12 23:46, scameron@beardog.cce.hp.com wrote: > I would be curious to see what kind of results you would get with scsi_debug > with fake_rw=1. I am sort of suspecting that trying to put an "upper limit" > on scsi LLD IOPS performance by seeing what scsi_debug will do with fake_rw=1 > is not really valid (or, maybe I'm doing it wrong) as I know of one case in > which a real HW scsi driver beats scsi_debug fake_rw=1 at IOPS on the very > same system, which seems like it shouldn't be possible. Kind of mysterious. The test # disable-frequency-scaling # modprobe scsi_debug delay=0 fake_rw=1 # echo 2 > /sys/block/sdc/queue/rq_affinity # echo noop > /sys/block/sdc/queue/scheduler # echo 0 > /sys/block/sdc/queue/add_random results in about 800K IOPS for random reads on the same setup (with a request size of 4 KB; CPU: quad core i5-2400). Repeating the same test with fake_rw=0 results in about 651K IOPS. Bart.