From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754992Ab1HZNZZ (ORCPT ); Fri, 26 Aug 2011 09:25:25 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:38327 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754029Ab1HZNZY (ORCPT ); Fri, 26 Aug 2011 09:25:24 -0400 Message-ID: <4E579E9F.9090906@linux.vnet.ibm.com> Date: Fri, 26 Aug 2011 08:24:47 -0500 From: Seth Jennings User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.20) Gecko/20110805 Thunderbird/3.1.12 MIME-Version: 1.0 To: Dan Magenheimer CC: Nebojsa Trpkovic , linux-kernel@vger.kernel.org, Konrad Wilk , Andrew Morton , Nitin Gupta Subject: Re: cleancache can lead to serious performance degradation References: <4E4C395E.20000@gmail.com 20110825041212.GA5014@dumpdata.com> <3aef71a8-d390-4a91-bfef-561c89edc040@default> In-Reply-To: <3aef71a8-d390-4a91-bfef-561c89edc040@default> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/25/2011 11:56 AM, Dan Magenheimer wrote: > Third, zcache is relatively new and can certainly benefit from > the input of other developers. The lzo1x compression in the kernel > is fairly slow; Seth Jennings (cc'ed) is looking into alternate > compression technologies. Perhaps there is a better compression > choice more suitable for older-slower processors, probably with a > poorer compression ratio. Further, zcache currently does compression > and decompression with interrupts disabled, which may be a > significant factor in the slowdowns you've observed. This should > be fixable. This was something I've meaning to ask about. Why are compression and decompression done with interrupts disabled? What would need to change so that we don't have to disable interrupts? >>> I guess that possible workaround could be to implement some kind of >>> compression throttling valve for cleancache/zcache: >>> >>> - if there's available CPU time (idle cycles or so), then compress >>> (maybe even with low CPU scheduler priority); > > Agreed, and this low-priority kernel thread ideally would also > solve the "compress while irqs disabled" problem! -- Seth