From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: How to determine performance bottleneck? Date: Tue, 14 Oct 2008 08:25:22 +0900 Message-ID: <48F3D8E2.8000006@kernel.org> References: <20081013202836.3fc62c3e@mjolnir.drzeus.cx> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:32996 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932146AbYJMX1d (ORCPT ); Mon, 13 Oct 2008 19:27:33 -0400 In-Reply-To: <20081013202836.3fc62c3e@mjolnir.drzeus.cx> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Pierre Ossman Cc: Jeff Garzik , linux-ide@vger.kernel.org Pierre Ossman wrote: > I'm playing around with performance tuning my disk access, but there is > something limiting my bandwidth to the disks. I was hoping you could > help me determine what. > > My setup is a sil3132 controller, connected to a PMP with five disks > behind it. I'm using iostat to measure disk traffic and I'm using reads > via dd for testing. > > When I'm accessing a single disk, the bandwidth is 70 - 80 MiB/s. When > I access a second disk, the bandwidth is about 50 MiB/s/disk, and all > five results in 25 MiB/s/disk. In other words, something is limiting > things to about 100 MiB/s. Now the question is what that limiting > factor is. > > The PCIe bus can sustain 250 MiB/s, so even with overhead that should > be plenty. The SATA links are in theory 300 MiB/s, so that can't be it > either. The remaining factors are the controller and the multiplier > chip, and/or the way we access them. > > Tejun, what kind of throughput have you seen when you have been testing > the sil3132 and multipliers? That's the limit of sil3124/3132. Dunno why but you can't go over that. There's 3132-2 chip on the market. Maybe it's worth a try? -- tejun