Date: Fri, 13 Jan 2006 10:55:33 -0800
From: thockin@hockin.org
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: Dual core Athlons and unsynced TSCs
Message-ID: <20060113185533.GA18301@hockin.org>
References: <1137104260.2370.85.camel@mindpipe> <20060113180620.GA14382@hockin.org> <1137175117.15108.18.camel@mindpipe> <20060113181631.GA15366@hockin.org> <1137175792.15108.26.camel@mindpipe>
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On Fri, Jan 13, 2006 at 01:09:51PM -0500, Lee Revell wrote:
> > Some apps/users need higher resolution and lower overhead that only rdtsc
> > can offer currently.
> 
> But obviously if the TSC gives wildly inaccurate results, it cannot be
> used no matter how low the overhead.

unless we can re-sync the TSCs often enough that apps don't notice.

> > I never tried it with pmtimer, we had HPET available.  Empirically TSC did
> > not work (and we had a simple test case to show how bad it could get).
> > HPET made that go away for users of gettimeofday().
> > 
> > We're exploring rdtsc-compatible solutions.
> > 
> 
> Since timekeeping on these machines has always been completely broken,
> shouldn't the default time source have been changed to the PM timer or
> HPET as soon as the problem was known?

If you have HPET, the kernel will prefer that.  I don't know enough about
the PMtimer overhead or resolution to say for sure.
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