Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753992AbZCIKue (ORCPT ); Mon, 9 Mar 2009 06:50:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752891AbZCIKuZ (ORCPT ); Mon, 9 Mar 2009 06:50:25 -0400 Received: from brick.kernel.dk ([93.163.65.50]:57824 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752549AbZCIKuZ (ORCPT ); Mon, 9 Mar 2009 06:50:25 -0400 Date: Mon, 9 Mar 2009 11:50:22 +0100 From: Jens Axboe To: Geert Uytterhoeven 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 Message-ID: <20090309105022.GN11787@kernel.dk> References: <20090305110940.GY11787@kernel.dk> <20090306074639.GN11787@kernel.dk> <20090306125832.GX11787@kernel.dk> <20090306190350.GD11787@kernel.dk> <20090309104833.GM11787@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090309104833.GM11787@kernel.dk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2917 Lines: 58 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 the old driver in another directory :-) -- 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/