From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753405Ab0IHNrv (ORCPT <rfc822;w@1wt.eu>);
	Wed, 8 Sep 2010 09:47:51 -0400
Received: from gw1.transmode.se ([213.115.205.20]:46516 "EHLO gw1.transmode.se"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750847Ab0IHNrs (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 8 Sep 2010 09:47:48 -0400
In-Reply-To: <1283950818.23762.20.camel@laptop>
References: <OF71DD00AE.26643E4D-ONC1257798.00250630-C1257798.002A9748@transmode.se>	 <1283932600.2880.1.camel@edumazet-laptop>
	 <OF5074952F.1B97B2B8-ONC1257798.002C51D7-C1257798.002C63A4@transmode.se>
	 <1283934289.2880.12.camel@edumazet-laptop>	 <OF2B75FA7C.7064BC41-ONC1257798.00318FDA-C1257798.00329AEF@transmode.se>
	 <alpine.LFD.2.00.1009081143200.2477@localhost6.localdomain6>	 <OF82705D74.3C13AE80-ONC1257798.00427DAB-C1257798.0042F243@transmode.se>
	 <alpine.LFD.2.00.1009081442390.2477@localhost6.localdomain6> <1283950818.23762.20.camel@laptop>
Subject: Re: slow nanosleep?
X-KeepSent: A5A9E9D0:0B55FA15-C1257798:004A7BB3;
 type=4; name=$KeepSent
To: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>, linux-kernel@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>
X-Mailer: Lotus Notes Release 8.5.2 August 10, 2010
Message-ID: <OFA5A9E9D0.0B55FA15-ONC1257798.004A7BB3-C1257798.004B86F2@transmode.se>
From: Joakim Tjernlund <joakim.tjernlund@transmode.se>
Date: Wed, 8 Sep 2010 15:44:57 +0200
X-MIMETrack: Serialize by Router on sesr04/Transmode(Release 8.5.1FP3|May 23, 2010) at
 2010-09-08 15:47:47
MIME-Version: 1.0
Content-type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Peter Zijlstra <peterz@infradead.org> wrote on 2010/09/08 15:00:18:
>
> On Wed, 2010-09-08 at 14:43 +0200, Thomas Gleixner wrote:
> > > However nanosleep with 1 ns and prctl(PR_SET_TIMERSLACK, 1) takes
> > > about 8 us on x86(Intel(R) Core(TM)2 Duo CPU E8500  @ 3.16GHz)
> > > and 20 us on my slower ppc board. Is that system call overhead
> > > or possibly some error?
> >
> > That's overhead I fear. We go way up to enqueue/arm the timer until we
> > figure out that the timeout already happened.
>
> Well, there's also the fact that his ppc board is simply dead slow,
> using the freq ratio: 3166/266 you'd expect (at a similar ins/clock
> ratio) the ppc to take 95us.
>
> So in fact the pcc taking 20us is actually quite good.

Actually, it takes 120 us. The 20 us was when I had Thomas
timeout == 0 fast path patch applied(forgot to remove it).
Without that patch it takes about 115 us. So it seems it takes
115-20=95 us to turn the timer wheel on my ppc.

 Jocke