From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754956AbYANGYt (ORCPT ); Mon, 14 Jan 2008 01:24:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751699AbYANGYm (ORCPT ); Mon, 14 Jan 2008 01:24:42 -0500 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:57678 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751583AbYANGYl (ORCPT ); Mon, 14 Jan 2008 01:24:41 -0500 Date: Mon, 14 Jan 2008 17:24:32 +1100 From: David Chinner To: Matthias Schniedermeyer Cc: linux-kernel@vger.kernel.org Subject: Re: Why is deleting (or reading) files not counted as IO-Wait in top? Message-ID: <20080114062432.GN155259@sgi.com> References: <20080102193503.GA31414@citd.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080102193503.GA31414@citd.de> User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 02, 2008 at 08:35:03PM +0100, 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. Simply because the only I/O that XFS does during a delete is to the log and the log does async I/O and hence the process never blocks in I/O. Instead, it blocks in a far more complex space reservation that may or may not be related to I/O wait.... > So, as 'rm -rf' is essentially a IO (or seek, to be more correct)-bound > task, shouldn't that count as "Waiting for IO"? rm -rf is not seek bound on XFS - it's generally determined by the sequential write speed of the block device or how fast your CPU is.... > The man-page of top says: > 'Amount of time the CPU has been waiting for I/O to complete.' Async I/O means that typically your CPU does not get held up waiting for I/O to complete.... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group