From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755204AbZFPTPO (ORCPT ); Tue, 16 Jun 2009 15:15:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754190AbZFPTPC (ORCPT ); Tue, 16 Jun 2009 15:15:02 -0400 Received: from main.gmane.org ([80.91.229.2]:35987 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753107AbZFPTPB (ORCPT ); Tue, 16 Jun 2009 15:15:01 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Jason Lynch Subject: [BUG?,FEATURE?] One core idles with 4 nice and 1 regular process Date: Tue, 16 Jun 2009 19:09:59 +0000 (UTC) Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 207-118-117-152.dyn.centurytel.net User-Agent: Pan/0.133 (House of Butterflies) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org First, a description of the problem, and a fairly simple way to test it: All of this is running on my quad-core Q6600. First, I start four nice -n 19 processes, each of which does nothing but busy-wait. (In my case, I used a simple python script, but any CPU-bound process will do.) At this point, top shows all four cores being utilized, at approximately 100% nice each. At this point, I start another of these busy-waiting processes, except with no nice adjustment, so it runs at regular priority. After doing so, top now reports the following CPU usage: one core is 100% user, two cores are 100% nice, and finally, one last core is 100% idle, doing nothing, despite a total of five processes being available to run. I thought I first noticed this running a 2.6.29 kernel, and thought about bisecting, but my test 2.6.28 kernel also exhibited the behavior. I couldn't test any previous kernels due to a lack of ext4 support. Both my current 2.6.30 kernel and the torvalds/linux-2.6.git HEAD also show the behavior. Now, I'm not sure if this is a bug or a strange feature (though it seems very bug-like to me) or perhaps a configuration problem, but I'd like to find out nonetheless. If I can provide any additional information to help, I'll be happy to oblige.