Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759698AbZCBSzz (ORCPT ); Mon, 2 Mar 2009 13:55:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758612AbZCBSzc (ORCPT ); Mon, 2 Mar 2009 13:55:32 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:45343 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758572AbZCBSza (ORCPT ); Mon, 2 Mar 2009 13:55:30 -0500 Date: Mon, 2 Mar 2009 10:54:35 -0800 (PST) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Vadim Lobanov cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , lkml , linux-arch , Andrew Morton Subject: Re: [RFC][PATCH] irq: remove IRQF_DISABLED In-Reply-To: <200903021045.20723.vlobanov@speakeasy.net> Message-ID: References: <1235996477.5330.174.camel@laptop> <200903021045.20723.vlobanov@speakeasy.net> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1331 Lines: 32 On Mon, 2 Mar 2009, Vadim Lobanov wrote: > On Monday 02 March 2009 09:11:54 Linus Torvalds wrote: > > The thing is, with PIO, a 512-byte disk read ends up doing 256 16-bit word > > reads from the controller, each potentially up to 600ns long (PIO0 > > timings). That's 150ms - for a single sector! > > Out of curiosity, the peanut gallery wishes to ask: > Is the above supposed to be 600us (*1000), or 150us (/1000)? Probably the > latter. Sorry, I was off by a lot. Yes. /1000. The end result ends up being lots better (and I should have realized I did my conversion wrong, because the times ended up being _so_ big), but not better enough - we've had dropped timer interrupts etc on those kinds of machines unless you use "hdparm -u1". Although it porbably does mean that the problem tends to be more in the really bad mode0 case (600ns -> 150us/sector -> milliseconds for multi-sector transfers). I forget what our multi-sector limit is, I think it tends to be 16. So you'll never get _really_ long irq-off times, but "several ms" is still pretty damn bad. Linus -- 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/