From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751632Ab0KQXo2 (ORCPT ); Wed, 17 Nov 2010 18:44:28 -0500 Received: from fep17.mx.upcmail.net ([62.179.121.37]:39786 "EHLO fep17.mx.upcmail.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750722Ab0KQXo1 (ORCPT ); Wed, 17 Nov 2010 18:44:27 -0500 X-SourceIP: 80.56.199.130 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: <20101117153827.e9f169d1.akpm@linux-foundation.org> References: <20101117042720.033773013@intel.com> <20101117042850.002299964@intel.com> <20101117150837.a18d56c1.akpm@linux-foundation.org> <1290036299.2109.1288.camel@laptop> <20101117153827.e9f169d1.akpm@linux-foundation.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 18 Nov 2010 00:43:32 +0100 Message-ID: <1290037412.24491.11.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit X-Cloudmark-Analysis: v=1.1 cv=HQ3F56nxkum+cgCiDL7AXQpbvw7DWrWCBJRnYYnM0Zc= c=1 sm=0 a=KErA6q9OHrUA:10 a=IkcTkHD0fZMA:10 a=QyXUC8HyAAAA:8 a=J_RJI74puKMc2kXeYKwA:9 a=FWwI62vKsUR9TZ4hV5Qt65149XsA:4 a=QEXdDO2ut3YA:10 a=dGJ0OcVc7YAA:10 a=HpAAvcLHHh0Zw7uRqdWCyQ==:117 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2010-11-17 at 15:38 -0800, Andrew Morton wrote: > On Thu, 18 Nov 2010 00:24:59 +0100 > Peter Zijlstra wrote: > > > 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. > > grep -r "[^a-zA-Z0-9_]HZ[ ]*/[ ]*100[^0-9]" . Maybe they've got a patch-kit somewhere,. I'll ask around. It would be nice to have that sorted. 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 00:43:32 +0100 Message-ID: <1290037412.24491.11.camel@twins> References: <20101117042720.033773013@intel.com> <20101117042850.002299964@intel.com> <20101117150837.a18d56c1.akpm@linux-foundation.org> <1290036299.2109.1288.camel@laptop> <20101117153827.e9f169d1.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit 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: <20101117153827.e9f169d1.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Wed, 2010-11-17 at 15:38 -0800, Andrew Morton wrote: > On Thu, 18 Nov 2010 00:24:59 +0100 > Peter Zijlstra wrote: > > > 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. > > grep -r "[^a-zA-Z0-9_]HZ[ ]*/[ ]*100[^0-9]" . Maybe they've got a patch-kit somewhere,. I'll ask around. It would be nice to have that sorted. -- 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