From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752418Ab0C2OLd (ORCPT ); Mon, 29 Mar 2010 10:11:33 -0400 Received: from ppa04.Princeton.EDU ([128.112.128.215]:37070 "EHLO ppa04.Princeton.EDU" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751156Ab0C2OLb (ORCPT ); Mon, 29 Mar 2010 10:11:31 -0400 Date: Mon, 29 Mar 2010 10:11:06 -0400 From: Yury Polyanskiy To: john stultz Cc: Joel Becker , linux-kernel@vger.kernel.org, Andrew Morton , Jan Glauber Subject: Re: [PATCH] hangcheck-timer is broken on x86 Message-ID: <20100329101106.3678a312@penta.localdomain> In-Reply-To: <1269824436.1880.2.camel@work-vm> References: <20100323233611.6dcbe4f4@penta.localdomain> <20100326214648.GF9984@mail.oracle.com> <1269824436.1880.2.camel@work-vm> X-Mailer: Claws Mail 3.7.5 (GTK+ 2.18.6; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_//xQurcI4HTn3R_LdzFsLUTm"; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_//xQurcI4HTn3R_LdzFsLUTm Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable On Sun, 28 Mar 2010 18:00:36 -0700 john stultz wrote: > > 1) Does getrawmonotonic() satisfy hangcheck-timer? What I mean is, will > > it always return the wallclock nanoseconds even in the face of CPU speed > > changes, suspend, udelay, or any other suspension of kernel operation? > > Yes, I know this is a tougher standard than rdtsc(), but this is what > > hangcheck-timer wants. rdtsc() at least satisfied udelay and PCI hangs. >=20 > getrawmonotonic() can be stalled and will wrap on some hardware (acpi pm > timer wraps every 5 seconds). >=20 I am not sure which archs do you mean. But in any case, getrawmonotonic() is not just a wrap around a call to rdtsc() (or acpi pm timer read). It is based on the clock->raw_time, which is updated every timer interrupt by the update_wall_time(). So even if underlying timer wraps, it doesn't lead to getrawmonotonic() returning 0 sec. Y --Sig_//xQurcI4HTn3R_LdzFsLUTm Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iEYEARECAAYFAkuwtPoACgkQemuRe3zuqOTSfACcCKDLFECg2YSWQe2J18kJZ7pe OSMAnibaIvJLh7vfVqlOHJUQq4yIKf+c =Myw7 -----END PGP SIGNATURE----- --Sig_//xQurcI4HTn3R_LdzFsLUTm--