linux-kernel - Re: [PATCH 0/3] Improve TSC as a clocksource under VMware

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Message-Id: <1224607688.6161.25.camel@alok-dev1>
Date:	Tue, 21 Oct 2008 09:48:08 -0700
From:	Alok Kataria <akataria@...are.com>
To:	Pavel Machek <pavel@...e.cz>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Daniel Hecht <dhecht@...are.com>
Subject: Re: [PATCH 0/3] Improve TSC as a clocksource under VMware

On Tue, 2008-10-21 at 02:50 -0700, Pavel Machek wrote:
> > Hi,
> >
> > This patch set makes some changes to the TSC code, so that it is always
> > used as the default clocksource when running under VMware.
> > The first 2 patches do the ground work of adding code to detect if we
> > are running under VMware.
> > The third patch adds a tsc_reliable flag which tells us that TSC is
> > reliable on this system, so that we can skip some tests which can
> > potentially mark TSC as unstable. Details under individual patch
> > headers.
> 
> How do you _know_ TSC is stable under VMWare? 

Since we implement it that way :)
The hypervisor takes care of providing a constant rate TSC to the guest
on such systems which have variable frequency.

Thanks,
Alok

> AFAICT, accesses to TSC
> are not virtualized and system VMWare runs on may still use frequency
> scaling, no?
>                                                                         Pavel
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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