From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id F3801DDDF6 for ; Tue, 13 Mar 2007 18:12:21 +1100 (EST) Subject: Re: [PATCH] ppc: Add support for bigger page sizes than 4KB on PPC44x From: Benjamin Herrenschmidt To: Stefan Roese In-Reply-To: <200703122254.27087.sr@denx.de> References: <200703122254.27087.sr@denx.de> Content-Type: text/plain Date: Tue, 13 Mar 2007 08:12:14 +0100 Message-Id: <1173769934.24454.67.camel@localhost.localdomain> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2007-03-12 at 22:54 +0100, Stefan Roese wrote: > This patch adds support for the PAGE_SIZE set equal to 64 KB on > PPC32 platforms. Increasing the PAGE_SIZE may improve the performance > of the system in some cases. > > The RAID processing with the dedicated hardware that offloads the CPU > is one of such cases. Using the bigger PAGE_SIZE we decrease the number > of CPU operations required to process the data blocks, decrease the > control overheads and so improve the overall performance. For example, > changing the PAGE_SIZE from 4KB to 64KB on a Yucca (440SPe) gives ~300% > performance benefit of the full-stripe writing in the (7d+1p) RAID-5 > setup. > > Signed-off-by: Yuri Tikhonov > Acked-by: Wolfgang Denk > Acked-by: Stefan Roese While it's a good idea, there are a couple of issues with the patch: - It's arch/ppc. We shouldn't do new major features on this codebase. You are welcome however in helping moving over 4xx to arch/powerpc :-) - You only adapted head_4xx.S but the config option is global to all of arch/ppc, thus changing it will probably break everything else. Make sure the option is done in such a way that it can't be changed or the kernel doesn't build if changed for a processor family where you haven't implemented the support - Have you tried other page sizes ? How hard would it be to support 16K and what kind of performance numbers do you get with 16K ? It's a better compromise for some applications as 64K causes significant bloat of the page cache (among other things). Cheers, Ben.