From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753434AbXLCQ4d (ORCPT ); Mon, 3 Dec 2007 11:56:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751081AbXLCQ40 (ORCPT ); Mon, 3 Dec 2007 11:56:26 -0500 Received: from mx1.redhat.com ([66.187.233.31]:38746 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751012AbXLCQ4Z (ORCPT ); Mon, 3 Dec 2007 11:56:25 -0500 To: Miklos Szeredi Cc: zach.brown@oracle.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, jdike@addtoit.com, user-mode-linux-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [2.6.24 BUG] 100% iowait on host while UML is running X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? References: From: Jeff Moyer Date: Mon, 03 Dec 2007 11:55:16 -0500 In-Reply-To: (Miklos Szeredi's message of "Mon\, 03 Dec 2007 16\:32\:51 +0100") Message-ID: User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Miklos Szeredi writes: > On 2.6.24, top started showing 100% iowait on one CPU when a UML > instance was running (but completely idle). I've traced it to this > commit [1]. Reverting it cures the problem. Hi, The UML code sits in io_getevents waiting for an event to be submitted and completed. This is a case I completely overlooked when putting together the referenced patch. We could check ctx->reqs_active before scheduling to determine whether or not we are waiting for I/O, but this would require taking the context lock in order to be accurate. Given that the test would be only for the sake of book keeping, it might be okay to do it outside of the lock. Zach, what are your thoughts on this? -Jeff [1] commit 41d10da3717409de33d5441f2f6d8f072ab3fbb6