From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH 2/2] libata: micro-optimize tag allocation Date: Fri, 16 Jan 2015 16:17:21 -0700 Message-ID: <54B99C01.2030507@fb.com> References: <20150116231225.18771.75061.stgit@viggo.jf.intel.com> <20150116231307.18771.52330.stgit@viggo.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:43615 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752089AbbAPXRf (ORCPT ); Fri, 16 Jan 2015 18:17:35 -0500 In-Reply-To: <20150116231307.18771.52330.stgit@viggo.jf.intel.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Dan Williams , linux-ide@vger.kernel.org Cc: Tejun Heo , Shaohua Li , Christoph Hellwig On 01/16/2015 04:13 PM, Dan Williams wrote: > Jens notes, "libata tag allocator sucks. Like seriously sucks, it's > almost a worst case implementation." Previously I thought SATA mmio > latency dominated performance profiles, but as Tejun notes: > > "Hmmm... one problem with the existing tag allocator in ata is that > it's not very efficient which actually shows up in profile when libata > is used with a very zippy SSD. Given that ata needs a different > allocation policies anyway maybe the right thing to do is making the > existing allocator suck less." > > So replace it with a naive enhancement that also supports the existing > quirks. Hopefully, soon to be replaced by Shaohua's patches [1], but > those do not yet support the quirk needed by sil24 (ATA_FLAG_LOWTAG) > [2]. That's trivial to do, it's just always having '0' in the cache and that's where the search would start. -- Jens Axboe