From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [PATCH] 2.6.34-rc3 v2 Disable R_OK (Early ACK) on SII 3726 PMP Date: Thu, 22 Apr 2010 22:05:48 -0400 Message-ID: <4BD1007C.2000300@pobox.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-gw0-f46.google.com ([74.125.83.46]:64887 "EHLO mail-gw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755039Ab0DWCFu (ORCPT ); Thu, 22 Apr 2010 22:05:50 -0400 In-Reply-To: Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Grant Grundler Cc: Linux IDE mailing list , Tejun Heo , LKML On 04/14/2010 09:43 PM, Grant Grundler wrote: > In 2009, While running "cache read" performance test of drives behind > SII PMP we encountered a "all 5 drives" timeout on more than 30% of the > machines under test. This patch reduces the rate by a factor of about 70. > Low enough that we didn't care to further investigate the issue. > > Performance impact with any sort of "normal" use was ~2%+ CPU and less > than 1% throughput degradation. Worst case impact (cached read) was > 6% IOPS reduction. This is with NCQ off (q=1) but I believe FIS based > switching enabled in the SATA driver. > > The patch disables "Early ACK" in the 3726 port multiplier. > "Early ACK" is issued when device sends a FIS to the host (via PMP) > and the PMP sends an ACK immediately back to the device - well before > the host gets the response. Under worst case IOPs load (cached read > test) and more than 2 PMPs connected to a 4-port SATA controller, > I suspect the time to service all of the PMPs is exceeding the PMPs > ability to keep track of outstanding FIS it owes the Host. Reducing > the number of PMPs to 2 (or 1) reduces the frequency by several orders > of magnitude. Kudos to Gwendal for initial debugging of this issue. > [Any errors in the description are mine, not his.] > > Patch is currently in production on Google servers. > > Signed-off-by: Grant Grundler > Signed-off-by: Gwendal Grignou > Acked-by: Tejun Heo > > --- > > v2: dropped references to 4726 since I didn't test 4726, > moved register definition directly into libata-pmp.c, and > expanded the comment in the code to summarize the above description. > > Code below is white space mangled. Please use attached file. applied manually, please figure out a way to send patches that can be applied directly using the standard automated tools (== git am) that everyone uses