From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261211AbULUCnt (ORCPT ); Mon, 20 Dec 2004 21:43:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261266AbULUCnt (ORCPT ); Mon, 20 Dec 2004 21:43:49 -0500 Received: from web52606.mail.yahoo.com ([206.190.39.144]:38495 "HELO web52606.mail.yahoo.com") by vger.kernel.org with SMTP id S261211AbULUCnr (ORCPT ); Mon, 20 Dec 2004 21:43:47 -0500 Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; b=DgmsCMUqL6ivuMEQLxdx3CH/zGSDhD8fBzg/s8iJkcxdnRNMdW3+KRFyt9cT3imYMoGT7i+rB0mG65PUOxAW/nG7TGOYKtxHSIqGv2ipUfPOloMZfA6X/9ZHVsrtrrIRPypwBg1E8ndQdAD8nL0jd45EexEYrvBa2+dtHTkGdGY= ; Message-ID: <20041221024347.3004.qmail@web52606.mail.yahoo.com> Date: Mon, 20 Dec 2004 18:43:47 -0800 (PST) From: jesse Subject: Gurus, a silly question for preemptive behavior To: linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org As i know, in linux, user space application is preemptive at any time. however, linux kernel is NOT preemptive, that means, even some event is finished, Linux kernel scheduler itself still can't have opportunity to interrupt the current user application and switch it out. it is called scheduler latency. normally , the latency is about 88us in mean , maximum : 200ms. Thus, the short latency shouldn't impact user applications too much and is not a problem. It is an issue in those embedded voice processing systems by introducing jitters, thus smart people came up with two kernel schedule patch: preemptive patch and low latency patch. My application which has nice value as 10 of low priority, however, it holds the CPU and excludes other applciations that have higher priority (nice 0) to run, my application causes CPU pegging. Thus, I am wondering: why user space application can't be effectively interrupted? why there is CPU pegging? Could you please educate me on this particular issue and shed me some light to address it? my system: [root@sa-c2-7 proc]# uname -a Linux sa-c2-7 2.4.21-15.ELsmp #1 SMP Thu Apr 22 00:18:24 EDT 2004 i686 i686 i386 GNU/Linux thanks!