linux-kernel - Re: AMD X2 unsynced TSC fix?

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Message-Id: <200610281137.22451.ak@suse.de>
Date:	Sat, 28 Oct 2006 11:37:22 -0700
From:	Andi Kleen <ak@...e.de>
To:	Willy Tarreau <w@....eu>
Cc:	Lee Revell <rlrevell@...-job.com>, thockin@...kin.org,
	Luca Tettamanti <kronos.it@...il.com>,
	linux-kernel@...r.kernel.org, john stultz <johnstul@...ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?

On Friday 27 October 2006 22:28, Willy Tarreau wrote:
> On Fri, Oct 27, 2006 at 11:28:00PM -0400, Lee Revell wrote:
> > On Fri, 2006-10-27 at 18:04 -0700, Andi Kleen wrote:
> > > I don't think it makes too much sense to hack on pure RDTSC when
> > > gtod is fast enough -- RDTSC will be always icky and hard to use.
> >
> > I agree FWIW, our application would be happy to just use gtod if it
> > wasn't so slow on these machines.
>
> Agreed, I had to turn about 20 dual-core servers to single core because
> the only way to get a monotonic gtod made it so slow that it was not
> worth using a dual-core. 

Curious - what workload was that? 

While gtod is time critical and often appears high on profile lists it is 
normally not as time critical as you're claiming it is; especially not
time critical enough to warrant such radical action.

> I initially considered buying one dual-core 
> AMD for my own use, but after seeing this, I'm definitely sure I won't
> ever buy one as long as this problem is not fixed, as it causes too
> many problems.

It's somewhat slower, but I'm not sure what "too many problems" you're
refering to.

-Andi
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