From: Ingo Molnar <mingo@elte.hu>
To: Pete Wyckoff <pw@osc.edu>
Cc: dean gaudet <dean@arctic.org>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: nosmp/maxcpus=0 or 1 -> TSC unstable
Date: Wed, 16 Jan 2008 16:31:37 +0100 [thread overview]
Message-ID: <20080116153137.GA18553@elte.hu> (raw)
In-Reply-To: <20080115225039.GA25701@osc.edu>
* Pete Wyckoff <pw@osc.edu> wrote:
> > pretty sure this is the culprit is that num_possible_cpus() > 1,
> > which would mean cpu_possible_map contains the second cpu... but i'm
> > not quite sure what the right fix is... or perhaps this is all
> > intended.
>
> We've seen the same problem. We use gettimeofday() for timing of
> network-ish operations on the order of 10-50 us. But not having the
> TSC makes gettimeofday() itself very slow, on the order of 30 us.
30 usecs is too much - even with pmtimer it's typically below 5 usecs.
Could you run this on your box:
http://people.redhat.com/mingo/time-warp-test/time-warp-test.c
and send back what it reports? (run it for a few minutes)
Ingo
next prev parent reply other threads:[~2008-01-16 15:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-12 19:48 nosmp/maxcpus=0 or 1 -> TSC unstable dean gaudet
2008-01-15 22:50 ` Pete Wyckoff
2008-01-16 4:13 ` Andi Kleen
2008-01-16 15:31 ` Ingo Molnar [this message]
2008-01-16 16:24 ` Pete Wyckoff
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