Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758160Ab2BISH4 (ORCPT ); Thu, 9 Feb 2012 13:07:56 -0500 Received: from mail-pw0-f46.google.com ([209.85.160.46]:65049 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751927Ab2BISHz convert rfc822-to-8bit (ORCPT ); Thu, 9 Feb 2012 13:07:55 -0500 MIME-Version: 1.0 In-Reply-To: <20120209175948.GE19392@google.com> References: <20120206215451.GD21292@google.com> <4F30C96F.1000905@kernel.dk> <20120207162253.GG21292@google.com> <4F315113.5010804@kernel.dk> <20120207164735.GH21292@google.com> <20120208162925.GA19392@google.com> <20120209175948.GE19392@google.com> From: Linus Torvalds Date: Thu, 9 Feb 2012 10:07:35 -0800 X-Google-Sender-Auth: aBIup4S60mVjmw46X3VtBHnKRHo Message-ID: Subject: Re: [PATCH] block: strip out locking optimization in put_io_context() To: Tejun Heo Cc: Shaohua Li , Jens Axboe , Vivek Goyal , lkml , Knut Petersen , mroos@linux.ee Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1089 Lines: 24 On Thu, Feb 9, 2012 at 9:59 AM, Tejun Heo wrote: > > * What exactly is the test and what do you measure? ?What does "12% > ?regression" mean? ?Is it wallclock time or CPU time? ?If it's CPU > ?time, does systime increase dominate the regression? Shaohua, it might be interesting to see a profile of the bad case. Now, quite often these kinds of things don't show anything at all - it's just due to cache issues and there's no obvious "we hold spinlock X for 15 seconds total". But if it's actual lock contention rather than just "more scheduling of worker threads", it should show up in the profile quite clearly. That said, I do think the RCU approach is the right one. The whole delayed deallocation (and the replacement patch with rwlocks) really smells like "badly done RCU-like behavior" to me. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/