Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753859AbZCIKwY (ORCPT ); Mon, 9 Mar 2009 06:52:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752594AbZCIKwP (ORCPT ); Mon, 9 Mar 2009 06:52:15 -0400 Received: from vervifontaine.sonytel.be ([80.88.33.193]:63982 "EHLO vervifontaine.sonycom.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752549AbZCIKwP (ORCPT ); Mon, 9 Mar 2009 06:52:15 -0400 Date: Mon, 9 Mar 2009 11:52:12 +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: <20090309105022.GN11787@kernel.dk> Message-ID: References: <20090305110940.GY11787@kernel.dk> <20090306074639.GN11787@kernel.dk> <20090306125832.GX11787@kernel.dk> <20090306190350.GD11787@kernel.dk> <20090309104833.GM11787@kernel.dk> <20090309105022.GN11787@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: 3492 Lines: 77 On Mon, 9 Mar 2009, Jens Axboe wrote: > On Mon, Mar 09 2009, Jens Axboe wrote: > > On Mon, Mar 09 2009, Geert Uytterhoeven wrote: > > > 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 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. > > > > > > > > Ah right, I hadn't looked close enough. But putting the mutex_lock() > > > > outside of the bio_for_each_segment() is going to be much faster than > > > > getting/releasing it for each segment. > > > > > > It doesn't seem to make any measurable difference, so I'm gonna leave it for > > > now. > > > > It will depend on where the bio's are coming from. If they are all > > single segment, then there will be no difference. If they contain > > multiple segments, you reduce the lock/release by that amount. > > > > But yeah, just leave it as-is for now. You can send a final patch for > > inclusion though. Unless I'm mistaken, I only saw the original and then > > an incremental patch for changing it to ->make_request_fn? > > There was a full version, my mistake. I got confused by the removal of Indeed. > the old driver in another directory :-) Can you please ack it? Thx! 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/