Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755818AbYACAQ7 (ORCPT ); Wed, 2 Jan 2008 19:16:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753169AbYACAQw (ORCPT ); Wed, 2 Jan 2008 19:16:52 -0500 Received: from ug-out-1314.google.com ([66.249.92.172]:12723 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752891AbYACAQv (ORCPT ); Wed, 2 Jan 2008 19:16:51 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:subject:date:user-agent:cc:references:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:message-id; b=SYDugeE++2YzgdO8s+cQjZDp5qlWs/gUoTA+SJyaEt4Jf269iZRN38h6qg46vqWY7EunUpW8LTqkyuo62G3WENRTi/kZx4xn4vY8u7epefJK3/2oHfyjPfmqjjeHQumL5MmLD61B3xpp+Qv0FuuRcrMQXC7WTiRuPvRb2vHMBBc= From: Maxim Levitsky To: Matthias Schniedermeyer Subject: Re: Why is deleting (or reading) files not counted as IO-Wait in top? Date: Thu, 3 Jan 2008 02:16:44 +0200 User-Agent: KMail/1.9.6 (enterprise 0.20071204.744707) Cc: linux-kernel@vger.kernel.org References: <20080102193503.GA31414@citd.de> In-Reply-To: <20080102193503.GA31414@citd.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200801030216.44446.maximlevitsky@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1531 Lines: 44 On Wednesday, 2 January 2008 21:35:03 Matthias Schniedermeyer wrote: > Hi > > > Currently i'm deleting about 500.000 files on a XFS-filesystem which > takes a few minutes, as i had a top open i saw that 'wa' is shown as > 0.0% (Nothing else running currently) and everything except 'id' is near > the bottom too. Kernel is 2.6.23.11. > > So, as 'rm -rf' is essentially a IO (or seek, to be more correct)-bound > task, shouldn't that count as "Waiting for IO"? > > The man-page of top says: > 'Amount of time the CPU has been waiting for I/O to complete.' > > But AFAICT wa only seams to be (ac)counted for writing and not for > reading. I come to that conclusion because, when i fire 'sync' i can see > some percent wa for a few seconds. > > > > > Bis denn > The IOWAIT time is the IDLE time that was spent waiting for I/O. (meaning that there were no tasks running, but some were waiting on I/O) Thus if you have another task that is not I/O bound, it can run in that time, and ideally, you shouldn't notice any I/O slowdown, but the iowait time will decrease. It wasn't the case before CFS introduction. I did few tests that showed almost 50% slowdown when running another task in that iowait time. It is not longer a problem with CFS. Regards, Maxim Levitsky -- 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/