From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754884Ab0INUSY (ORCPT ); Tue, 14 Sep 2010 16:18:24 -0400 Received: from icebox.esperi.org.uk ([81.187.191.129]:40201 "EHLO mail.esperi.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751490Ab0INUSX (ORCPT ); Tue, 14 Sep 2010 16:18:23 -0400 To: Thomas Gleixner Cc: Artur Skawina , Venkatesh Pallipadi , Damien Wyart , John Drescher , Suresh Siddha , LKML , "H. Peter Anvin" Subject: Re: [BISECTED] 2.6.35.*: horrible (exponential? >linear) slowdown to unusability (HPET) References: <87eid282pj.fsf@spindle.srvr.nix> From: Nix Emacs: a real time environment for simulating molasses-based life forms. Date: Tue, 14 Sep 2010 21:17:59 +0100 In-Reply-To: (Thomas Gleixner's message of "Tue, 14 Sep 2010 12:09:57 +0200 (CEST)") Message-ID: <878w34qdu0.fsf@spindle.srvr.nix> User-Agent: Gnus/5.1008 (Gnus v5.10.8) XEmacs/21.5-b29 (linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-DCC-URT-Metrics: spindle 1060; Body=8 Fuz1=8 Fuz2=8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14 Sep 2010, Thomas Gleixner said: > On Fri, 10 Sep 2010, Thomas Gleixner wrote: >> On Fri, 10 Sep 2010, Nix wrote: >> > >> > I suspect current_clocksource doesn't do what we think it does, or the >> > clocksource and 'clock event device' are not the same.) >> >> Right, they are not the same. clocksource provides us a read out >> device for timekeeping (usually a simple increasing counter). clock >> event device is used to generate timer interrupts. >> >> HPET provides both functionalities. >> >> The patch you bisected is affecting the clock events part of the >> HPET. So yes, it's not a clock source problem. > > Another question. If you add hpet=verbose (or revert that commit) does > the printk_once in hpet_set_next_event() show up in dmesg ? > > "hpet: compare register read back failed." Well, given that I reverted that commit in the past (during the bisection) and also added hpet=verbose[1], I'd have expected it to turn up in my past syslogs. There is no sign of it, in syslogs back to 2009. [1] and indeed am running 2.6.35.4 with hpet=verbose and no symptoms on the affected system *now* -- a mystery because I thought the hpet=verbose-turns-it-off code was removed, but turning on verbose still seems to quash the bug?! or perhaps it's slightly intermittent and every N boots I'm lucky enough to miss it. I'm slightly chary of rebooting to find out ;}