Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262254AbUKDPR5 (ORCPT ); Thu, 4 Nov 2004 10:17:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262261AbUKDPQM (ORCPT ); Thu, 4 Nov 2004 10:16:12 -0500 Received: from mx1.elte.hu ([157.181.1.137]:61408 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S262257AbUKDPPm (ORCPT ); Thu, 4 Nov 2004 10:15:42 -0500 Date: Thu, 4 Nov 2004 16:16:31 +0100 From: Ingo Molnar To: Mark_H_Johnson@raytheon.com Cc: Karsten Wiese , Bill Huey , Adam Heath , "K.R. Foley" , linux-kernel@vger.kernel.org, Florian Schmidt , Fernando Pablo Lopez-Lezcano , Lee Revell , Rui Nuno Capela , Thomas Gleixner , Michal Schmidt Subject: Re: [patch] Real-Time Preemption, -RT-2.6.10-rc1-mm2-V0.7.1 Message-ID: <20041104151631.GA24056@elte.hu> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-2.201, required 5.9, BAYES_00 -4.90, SORTED_RECIPS 2.70 X-ELTE-SpamLevel: X-ELTE-SpamScore: -2 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1136 Lines: 26 * Mark_H_Johnson@raytheon.com wrote: > Let me follow up briefly on the regression I noticed yesterday on ping > responses from an SMP system with one real time task running. [...] icmp/ping replies are handled by ksoftirqd. Once a networking request has been handed to ksoftirqd it cannot be redirected to another CPU, because softirq processing is fundamentally per-CPU. So if the network interrupt hits the CPU where the RT-task is running then the RT task will starve that ksoftirq instance (and hence the reply) even if another CPU in the system is idle. i agree that this is an SMP/RT artifact that should be fixed. hardirq workload can be redirected to other CPUs because it's single-threaded, but it's not that easy for softirq workload. i suspect the same phenomenon causes some of the other scheduling artifacts ('frozen' X) you've noticed. Ingo - 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/