From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750722AbVHXHIK (ORCPT ); Wed, 24 Aug 2005 03:08:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750770AbVHXHIK (ORCPT ); Wed, 24 Aug 2005 03:08:10 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:24244 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S1750722AbVHXHIJ (ORCPT ); Wed, 24 Aug 2005 03:08:09 -0400 Date: Wed, 24 Aug 2005 09:08:10 +0200 From: Jens Axboe To: Nathan Scott Cc: Linux Kernel Subject: Re: [PATCH] blk queue io tracing support Message-ID: <20050824070809.GA27956@suse.de> References: <20050823123235.GG16461@suse.de> <20050824010346.GA1021@frodo> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050824010346.GA1021@frodo> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 24 2005, Nathan Scott wrote: > On Tue, Aug 23, 2005 at 02:32:36PM +0200, Jens Axboe wrote: > > Hi, > > > > This is a little something I have played with. It allows you to see > > exactly what is going on in the block layer for a given queue. Currently > > it can logs request queueing and building, dispatches, requeues, and > > completions. > > Ah, fabulous. Thanks Jens! > > > + t.magic = BLK_IO_TRACE_MAGIC | BLK_IO_TRACE_VERSION; > > + t.sequence = atomic_add_return(1, &bt->sequence); > > + t.time = sched_clock() / 1000; > > Wouldn't it be better to pass out the highest precision available here > & then do the conversion in userspace instead? I guess one might want > that little bit more for a RAM disk or something ... actually, talking > to one of the SGI people here with alot of experience on IRIX with a > similar facility, the msec resolution there is apparently sometimes an > issue already with fast storage. This isn't msec precision, it's usec. sched_clock() is in ns! I already decided that msec is too coarse, but usec _should_ be enough. -- Jens Axboe