Messages in this thread |  | | | Date | Sun, 16 May 2010 13:29:33 -0700 | | From | Arjan van de Ven <> | | Subject | Re: [PATCH] x86: Export tsc related information in sysfs |
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On Sun, 16 May 2010 09:42:40 -0700 (PDT) Dan Magenheimer <dan.magenheimer@oracle.com> wrote:
> > From: Thomas Gleixner [mailto:tglx@linutronix.de] > > Nah, there are systems which will have it set to 1: > > Dig out your good old Pentium-I box and enjoy. > > Hot stove syndrome again? Are you truly saying that there > are NO single-socket multi-core systems that don't have > stupid firmware (SMI and/or BIOS)?
there are no systems *where we can know* this. Some of the stupid SMI only triggers on higher temperature situations etc. Impossible to know upfront.
> If things are this bad, why on earth would the kernel itself > EVER use TSC even as its own internal clocksource?
Why do you think we do extensive and continuous validation of the tsc (and soon, continuous recalibration)
> But that doesn't mean the vast majority of latest generation > single-socket systems can't set "tsc_reliable" to 1. Or that > the kernel is responsible for detecting and/or correcting > every system with buggy firmware.
sadly this also shows up on single socket systems... much more than we like.
This is why I really really hate having apps run tsc directly. A VDSO call at least gives the kernel the option to ensure correctness... even if it starts out fast and goes slow suddenly after 3 weeks when the AC in the datacenter got maintenance for an hour.
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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