Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751833AbZCKPqU (ORCPT ); Wed, 11 Mar 2009 11:46:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750769AbZCKPqJ (ORCPT ); Wed, 11 Mar 2009 11:46:09 -0400 Received: from cs20.apochromatic.org ([204.152.189.161]:58728 "EHLO cs20.apochromatic.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750764AbZCKPqI (ORCPT ); Wed, 11 Mar 2009 11:46:08 -0400 Date: Wed, 11 Mar 2009 15:46:05 +0000 From: Matt Fleming To: Wolfgang =?iso-8859-1?Q?M=FCes?= Cc: Pierre Ossman , Andrew Morton , David Brownell , Mike Frysinger , linux-kernel@vger.kernel.org Subject: Re: [PATCH 5/7] mmc_spi: allow higher timeouts for SPI mode Message-ID: <20090311154605.GD1475@console-pimps.org> References: <20090311140219.GA1475@console-pimps.org> <200903111555.00982.wolfgang.mues@auerswald.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <200903111555.00982.wolfgang.mues@auerswald.de> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1722 Lines: 41 On Wed, Mar 11, 2009 at 03:55:00PM +0100, Wolfgang M?es wrote: > > My patch 6 in mmc_spi_skip() is doing a busy-wait for a short while ( less > than 1 jiffie), and starts to call schedule() inside the loop if the card is > slower. > OK, but if my machine runs at 100 HZ then a jiffie is 10ms. Previously (without your patch) we waited for 300ms in the write case and 100ms in the read case. So, it's not unreasonable to think that a response is going to take more than 10ms. With your patch we're almost always going to schedule() with no indication of exactly when we're going to come back. > My goal was to avoid the long-lasting busy waiting. I have measured times up > to 900ms! With my patch, the longest busy waiting will be 1 jiffie. > I agree that busy-waiting for 900ms would be a bit mad. Is there a reason that you didn't implement this with msleep() as was noted in the comment above the timeout? /* REVISIT investigate msleep() to avoid busy-wait I/O * in at least some cases. */ > And yes, if the SD card is sending its response after 5 jiffies, it is > recognized only after the scheduler schedules this process, which will incure > a delay to the data transfer. The amount of delay is determined by the number > of running processes and the number of HZ. > Have you benchmarked this case? Do you know approximately how long it is before we return from the schedule() under various workloads? -- 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/