Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758150AbZFPL7X (ORCPT ); Tue, 16 Jun 2009 07:59:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753995AbZFPL7Q (ORCPT ); Tue, 16 Jun 2009 07:59:16 -0400 Received: from brick.kernel.dk ([93.163.65.50]:52116 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753437AbZFPL7P (ORCPT ); Tue, 16 Jun 2009 07:59:15 -0400 Date: Tue, 16 Jun 2009 13:59:17 +0200 From: Jens Axboe To: Steve Rottinger Cc: Leon Woestenberg , linux-kernel@vger.kernel.org Subject: Re: splice methods in character device driver Message-ID: <20090616115917.GX11363@kernel.dk> References: <4A0838D1.5090102@pentek.com> <20090511192253.GH4694@kernel.dk> <4A0AFC62.3090002@pentek.com> <20090604073218.GT11363@kernel.dk> <4A27CA0A.7060400@pentek.com> <4A32BE5B.7080503@pentek.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A32BE5B.7080503@pentek.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1414 Lines: 39 On Fri, Jun 12 2009, Steve Rottinger wrote: > Hi Leon, > > It does seem like a lot of code needs to be executed to move a small > chunk of data. It's really not, you should try and benchmark the function call overhead :-). > Although, I think that most of the overhead that I was experiencing > came from the cumulative > overhead of each splice system call. I increased my pipe size using > Jens' pipe size patch, > from 16 to 256 pages, and this had a huge effect -- the speed of my > transfers more than doubled. > Pipe sizes larger that 256 pages, cause my kernel to crash. Yes, the system call is more expensive. Increasing the pipe size can definitely help there. > I'm doing about 300MB/s to my hardware RAID, running two instances of my > splice() copy application > (One on each RAID channel). I would like to combine the two RAID > channels using a software RAID 0; > however, splice, even from /dev/zero runs horribly slow to a software > RAID device. I'd be curious > to know if anyone else has tried this? Did you trace it and find out why it was slow? It should not be. Moving 300MB/sec should not be making any machine sweat. -- Jens Axboe -- 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/