Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755889AbZFAHqT (ORCPT ); Mon, 1 Jun 2009 03:46:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755314AbZFAHqF (ORCPT ); Mon, 1 Jun 2009 03:46:05 -0400 Received: from mail-bw0-f222.google.com ([209.85.218.222]:45520 "EHLO mail-bw0-f222.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755279AbZFAHqE (ORCPT ); Mon, 1 Jun 2009 03:46:04 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=kp7mng3CFE4VEmF3le3G/tvT+kbaMIGgZCCHguwLyXI9aoryqvqeewjixtecsPtlFo 0DBQ9aiIUjg1YaHTYeIx3dE22YHSKYVxYmD2864CN/jW+ru+ZPH8tRDZY/q/wphaPWmi Abpc3SjuQQvsJcR/9rgvKmzi6t+SLc+r6Vjtk= MIME-Version: 1.0 In-Reply-To: <1243256510.26820.679.camel@twins> References: <63386a3d0905112337p2d426481o5f9bf9b9489cc57e@mail.gmail.com> <63386a3d0905231446h245bb4a9gec111f68a74a44e4@mail.gmail.com> <1243151839.26820.642.camel@twins> <63386a3d0905250513q6ca56eeepcf7bebe46c447fb4@mail.gmail.com> <1243256510.26820.679.camel@twins> Date: Mon, 1 Jun 2009 09:46:03 +0200 Message-ID: <63386a3d0906010046k3b86d70av3e290fc26c2934f5@mail.gmail.com> Subject: Re: [PATCH] U300 sched_clock implementation From: Linus Walleij To: Peter Zijlstra , Russell King - ARM Linux Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, linux-arm-kernel@lists.arm.linux.org.uk Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1772 Lines: 48 2009/5/25 Peter Zijlstra : > On Mon, 2009-05-25 at 14:13 +0200, Linus Walleij wrote: >> 2009/5/24 Peter Zijlstra : >> >> > On Sat, 2009-05-23 at 23:46 +0200, Linus Walleij wrote: >> > >> >> This overrides the global sched_clock() symbol in the Linux >> >> scheduler with a local implementation which takes advantage of >> >> the timesource in U300 giving a scheduling resolution of 1us. The >> >> solution is the same as found in the OMAP2 core code. >> > >> > We assume sched_clock() to return time in ns (e-9) resolution. >> >> Yep okay and in this case: >> >> >> + ret = (unsigned long long) u300_get_cycles(); >> >> + ret = (ret * clocksource_u300_1mhz.mult_orig) >> >> >> + clocksource_u300_1mhz.shift; >> >> + return ret; >> >> (mult_orig >> shift) == 1000 > > Ah, ok -- missed that little detail ;-) > >> So for each cycle in cyclecount register we return 1000 * cycles >> i.e 1000ns. >> >> If it looks nicer we can of course simply: >> return (unsigned long long) u300_get_cycles * 1000; >> >> But the question here is whether this resolution is enough for >> sched_clock() or if it is irrelevant to override sched_clock() >> if it cannot schedule with better precision than 1000 ns. > > No anything better than jiffies is good, 1us certainly is worth the > trouble. Can I interpret this as Acked-by: Peter Zijlstra ? Russell wanted an indication from the scheduler people that it looked sane... Yours, Linus Walleij -- 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/