Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754809AbZCFO0r (ORCPT ); Fri, 6 Mar 2009 09:26:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752702AbZCFO0i (ORCPT ); Fri, 6 Mar 2009 09:26:38 -0500 Received: from vervifontaine.sonytel.be ([80.88.33.193]:38976 "EHLO vervifontaine.sonycom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751001AbZCFO0h (ORCPT ); Fri, 6 Mar 2009 09:26:37 -0500 Date: Fri, 6 Mar 2009 15:26:34 +0100 (CET) From: Geert Uytterhoeven To: Jens Axboe cc: Benjamin Herrenschmidt , Jim Paris , Vivien Chappelier , David Woodhouse , Arnd Bergmann , Geoff Levand , Linux/PPC Development , Cell Broadband Engine OSS Development , Linux Kernel Development , linux-mtd@lists.infradead.org Subject: Re: [PATCH/RFC] ps3/block: Add ps3vram-ng driver for accessing video RAM as block device In-Reply-To: <20090306125832.GX11787@kernel.dk> Message-ID: References: <20090305083701.GQ11787@kernel.dk> <20090305110940.GY11787@kernel.dk> <20090306074639.GN11787@kernel.dk> <20090306125832.GX11787@kernel.dk> User-Agent: Alpine 2.00 (LRH 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-15 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2097 Lines: 49 On Fri, 6 Mar 2009, Jens Axboe wrote: > On Fri, Mar 06 2009, Geert Uytterhoeven wrote: > > On Fri, 6 Mar 2009, Jens Axboe wrote: > > > On Thu, Mar 05 2009, Geert Uytterhoeven wrote: > > > > But then I noticed ps3vram_make_request() may be called concurrently, > > > > so I had to add a mutex to avoid data corruption. This slows the > > > > driver down, and in the end, the version with a thread turns out to be > > > > ca. 1% faster. The version without a thread is about 50 lines less > > > > code, though. > > > > > > That is correct, ->make_request_fn may get reentered. I'm not surprised > > > that performance dropped if you just shoved everything under a mutex. > > > You could be a little more smart and queue concurrent bio's for > > > processing when the current one is complete though, there are several > > > approaches there that be a lot faster than going all the way through the > > > IO stack and scheduler just to avoid concurrency. > > > > Yes, using a spinlock and queueing requests on a list if the driver is > > busy can be done after 2.6.29... > > Certainly. Even just replacing your current mutex with a spinlock during > the memcpy() would surely be a lot faster. Or even just grabbing the > mutex before calling into the write for the duration of the bio. The way > you do it is certain context switch death :-) It's not just the memcpy(). ps3vram_{up,down}load() call msleep(), so I cannot use a spinlock. With kind regards, Geert Uytterhoeven Software Architect Sony Techsoft Centre Europe The Corporate Village ? Da Vincilaan 7-D1 ? B-1935 Zaventem ? Belgium Phone: +32 (0)2 700 8453 Fax: +32 (0)2 700 8622 E-mail: Geert.Uytterhoeven@sonycom.com Internet: http://www.sony-europe.com/ A division of Sony Europe (Belgium) N.V. VAT BE 0413.825.160 ? RPR Brussels Fortis ? BIC GEBABEBB ? IBAN BE41293037680010 -- 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/