From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932200Ab0JFNe4 (ORCPT ); Wed, 6 Oct 2010 09:34:56 -0400 Received: from casper.infradead.org ([85.118.1.10]:38522 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756315Ab0JFNey convert rfc822-to-8bit (ORCPT ); Wed, 6 Oct 2010 09:34:54 -0400 Subject: Re: 1 RT task blocks 4-core machine ? From: Peter Zijlstra To: Tommaso Cucinotta Cc: Dhaval Giani , Ingo Molnar , Thomas Gleixner , Dario Faggioli , Fabio Checconi , linux-kernel@vger.kernel.org In-Reply-To: <4CAA54A1.6050507@sssup.it> References: <4CAA54A1.6050507@sssup.it> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Wed, 06 Oct 2010 15:34:05 +0200 Message-ID: <1286372045.2144.180.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2010-10-05 at 00:26 +0200, Tommaso Cucinotta wrote: > A possible explanation might be that the CFS load balancing logic sees > my only active task (e.g., the ssh server or shell etc.) as running > alone on its core, and does not detect that it is inhibited to actually > run due to RT tasks on the same core. Therefore, it will not migrate > the task to the free cores. Does this explanation make sense > or is it completely wrong ? Possibly, its got some logic to detect this but maybe it gets confused still, in particular look at the adaptive cpu_power in update_cpu_power() and calling functions. > Also, I'd like to hear whether this is considered the "normal/desired" > behavior of intermixing RT and non-RT tasks. Pegging a cpu using sched_fifo/rr pretty much means you get to keep the pieces, if it works nice, if you can make it work better kudos, but no polling from sched_fifo/rr is not something that is considered sane for the general health of your system.