From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.multimedia-labs.de (mail.multimedia-labs.de [82.149.226.172]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mail.multimedia-labs.de", Issuer "Multimedia Labs CA" (not verified)) by ozlabs.org (Postfix) with ESMTP id 1C89E67A3F for ; Sat, 13 May 2006 00:55:00 +1000 (EST) Received: from localhost (localhost [127.0.0.172]) by mail.multimedia-labs.de (Postfix) with ESMTP id 5361F1C812E for ; Fri, 12 May 2006 16:22:49 +0200 (CEST) Received: from mail.multimedia-labs.de ([127.0.0.172]) by localhost (mail [127.0.0.172]) (amavisd-new, port 10024) with LMTP id 04386-01-2 for ; Fri, 12 May 2006 16:22:47 +0200 (CEST) Received: from xpc823.intern.randgruppe.info (e176171165.adsl.alicedsl.de [85.176.171.165]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.multimedia-labs.de (Postfix) with ESMTP id AAB5B1C80AF for ; Fri, 12 May 2006 16:22:47 +0200 (CEST) Received: from [10.0.0.75] (unknown [10.0.0.75]) by xpc823.intern.randgruppe.info (Postfix) with ESMTP id 1710270373 for ; Fri, 12 May 2006 16:23:54 +0200 (CEST) Message-ID: <44649A59.5050608@elitedvb.net> Date: Fri, 12 May 2006 16:23:21 +0200 From: Felix Domke MIME-Version: 1.0 To: linuxppc-dev Subject: Re: 2.6 vs 2.4 References: <7cb1293c0605112351y658460a0x8b793ea12004dbfc@mail.gmail.com> <1147442231.9412.9.camel@localhost.localdomain> In-Reply-To: <1147442231.9412.9.camel@localhost.localdomain> Content-Type: text/plain; charset=ISO-8859-1 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Benjamin Herrenschmidt wrote: >> Wolfgang Denk has a good listing of issues to consider betn linux 2.4 >>vs 2.6 for ppc82xx based platforms >>(http://www.denx.de/wiki/Know/Linux24vs26). >> Would this recommendation still hold? >> Are there any patches, developments in this area? > The main open question is: is somebody still maintaining the 8xx kernel > port ? The 4xx port has the same problem. When we switched from 2.4 to 2.6, IDE performance ("hdparm -t" to have a single number) was reduced by about 25% (even after trying to finetune the IDE driver - the time between the end of one transfer and the begin of the next transfer was just too long to saturate the harddisk). Because of my lack of knowledge of the block device layer's internals I wasn't able to track that down. My initial plan was to build a trace using the RiscTrace environment, to see any instruction executed between requests, but my company moved away from PPC4xx hardware (unfortunately), so I was never able to complete this. I still believe that other platforms have the same problems. On a 300MHz embedded mips machine, saturating a 100MBit network link via ftp is not easy. Our old 252MHZ PPC machines never performed better than around 5MB/s (but had a non-DMA NIC, which however could be satured in theory with about 70% cpu load, based on the bus bandwidth. Why are the remaining 30% not enough to do IDE DMA and the TCP overhead? Memory performance? But why did we had better numbers with 2.4 then?). On that mips machine, both IDE and network support DMA (agreed, it's a RTL8139, so it requires another memcpy), and memcpy() performance is >100MB/s. Where is the bottleneck? And, much more important: how do measure it? I'm sorry that I can't really much do anything else than complaining, but all my attempts to track down the problems were futile. I'm not sure if testing "ftp performance" (as a completely non-synthetic benchmark - FTP speed is/was a real issue on our platform) is "the right test", but it's one of the things where i personally want linux to become better. Or is this just a misconfiguration? Are there mysterious IO scheduler default parameters which are just suboptimal for our case? regards, Felix