Return-Path: <linux-kernel-owner+willy=40w.ods.org@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id <S268232AbTBYTYo>; Tue, 25 Feb 2003 14:24:44 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
	id <S268243AbTBYTYn>; Tue, 25 Feb 2003 14:24:43 -0500
Received: from bi01p1.co.us.ibm.com ([32.97.110.142]:11664 "EHLO w-patman.des")
	by vger.kernel.org with ESMTP id <S268232AbTBYTYm>;
	Tue, 25 Feb 2003 14:24:42 -0500
Date: Tue, 25 Feb 2003 11:24:58 -0800
From: Patrick Mansfield <patmans@us.ibm.com>
To: Andrew Morton <akpm@digeo.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.5.62-mm2 slow file system writes across multiple disks
Message-ID: <20030225112458.A5618@beaverton.ibm.com>
References: <20030224120304.A29472@beaverton.ibm.com> <20030224135323.28bb2018.akpm@digeo.com> <20030224174731.A31454@beaverton.ibm.com> <20030224204321.5016ded6.akpm@digeo.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <20030224204321.5016ded6.akpm@digeo.com>; from akpm@digeo.com on Mon, Feb 24, 2003 at 08:43:21PM -0800
Sender: linux-kernel-owner@vger.kernel.org
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1580
Lines: 38

On Mon, Feb 24, 2003 at 08:43:21PM -0800, Andrew Morton wrote:
> Patrick Mansfield <patmans@us.ibm.com> wrote:

> > I moved to 2.5.62-mm3 [I had to drop back to qlogicisp for my boot disk,
> > and run the feral drver as a module in order to boot without hanging], and
> > ran write-and-fsync with -f, with and without -o (O_DIRECT).

> Is this using an enormous request queue or really deep TCQ or something?
> I always turn TCQ off, stupid noxious thing it is.

Yes - pretty high, the feral driver is defaulting to 63 (comments there
say "FIX LATER"). Changing it to 8 gave much improved performance. 

I'm on a slightly different kernel, anyway:

10 fsync writes of 200 mb to 10 separate disks, queue depth (TCQ) of 63 gave:

0.05user 37.14system 1:09.39elapsed 53%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (1986major+3228minor)pagefaults 0swaps

10 fsync writes of 200 mb to 10 separate disks, queue depth of 8 gave:

0.05user 38.56system 0:32.71elapsed 118%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (1986major+3228minor)pagefaults 0swaps

The total time dropped by almost half. vmstat numbers were much smoother.

It would be nice if a larger queue depth did not kill performance.

The larger queue depths can be nice for disk arrays with lots of cache and
(more) random IO patterns.

-- Patrick Mansfield
-
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/