From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751214Ab0KQXZ6 (ORCPT ); Wed, 17 Nov 2010 18:25:58 -0500 Received: from canuck.infradead.org ([134.117.69.58]:41900 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750915Ab0KQXZ5 convert rfc822-to-8bit (ORCPT ); Wed, 17 Nov 2010 18:25:57 -0500 Subject: Re: [PATCH 06/13] writeback: bdi write bandwidth estimation From: Peter Zijlstra To: Andrew Morton Cc: Wu Fengguang , Jan Kara , Li Shaohua , Christoph Hellwig , Dave Chinner , "Theodore Ts'o" , Chris Mason , Mel Gorman , Rik van Riel , KOSAKI Motohiro , linux-mm , linux-fsdevel@vger.kernel.org, LKML In-Reply-To: <20101117150837.a18d56c1.akpm@linux-foundation.org> References: <20101117042720.033773013@intel.com> <20101117042850.002299964@intel.com> <20101117150837.a18d56c1.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 18 Nov 2010 00:24:59 +0100 Message-ID: <1290036299.2109.1288.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-11-17 at 15:08 -0800, Andrew Morton wrote: > On Wed, 17 Nov 2010 12:27:26 +0800 > Wu Fengguang wrote: > > > + w = min(elapsed / (HZ/100), 128UL); > > I did try setting HZ=10 many years ago, and the kernel blew up. > > I do recall hearing of people who set HZ very low, perhaps because > their huge machines were seeing performance prolems when the timer tick > went off. Probably there's no need to do that any more. > > But still, we shouldn't hard-wire the (HZ >= 100) assumption if we > don't absolutely need to, and I don't think it is absolutely needed > here. People who do cpu bring-up on very slow FPGAs also lower HZ as far as possible. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 06/13] writeback: bdi write bandwidth estimation Date: Thu, 18 Nov 2010 00:24:59 +0100 Message-ID: <1290036299.2109.1288.camel@laptop> References: <20101117042720.033773013@intel.com> <20101117042850.002299964@intel.com> <20101117150837.a18d56c1.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: Wu Fengguang , Jan Kara , Li Shaohua , Christoph Hellwig , Dave Chinner , Theodore Ts'o , Chris Mason , Mel Gorman , Rik van Riel , KOSAKI Motohiro , linux-mm , linux-fsdevel@vger.kernel.org, LKML To: Andrew Morton Return-path: In-Reply-To: <20101117150837.a18d56c1.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2010-11-17 at 15:08 -0800, Andrew Morton wrote: > On Wed, 17 Nov 2010 12:27:26 +0800 > Wu Fengguang wrote: >=20 > > + w =3D min(elapsed / (HZ/100), 128UL); >=20 > I did try setting HZ=3D10 many years ago, and the kernel blew up. >=20 > I do recall hearing of people who set HZ very low, perhaps because > their huge machines were seeing performance prolems when the timer tick > went off. Probably there's no need to do that any more. >=20 > But still, we shouldn't hard-wire the (HZ >=3D 100) assumption if we > don't absolutely need to, and I don't think it is absolutely needed > here. =20 People who do cpu bring-up on very slow FPGAs also lower HZ as far as possible. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org