Subject: Re: 2.6.15-rt4 failure with LATENCY_TRACE on x86_64
From: Steven Rostedt <rostedt@goodmis.org>
To: Clark Williams <williams@redhat.com>
Cc: lkml <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@elte.hu>
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Date: Fri, 13 Jan 2006 10:54:39 -0500
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On Fri, 2006-01-13 at 09:06 -0600, Clark Williams wrote:
> On Thu, 2006-01-12 at 22:18 -0500, Steven Rostedt wrote:
> > OK, I'm actually sending you this email on a x86_64 running
> > 2.6.15-rt4-sr2, with latency tracing on.  But unfortunately, I have a
> > AMD X2 that each core has it's own tsc counter that is not in sync, and
> > since the latency tracer uses tsc, I get garbage.  But beware, the tsc
> > does slow down when the cpu idles, so it gives bad results even for non
> > x2 systems.
> > 
> Hmm, I didn't realize that (I'm running on a uni-processor system). I
> just pulled your rt4-sr2 patch and will apply/rebuild/test. 
> 
> > I finally was able to boot this with using the PM timer, but the
> > beginning of my dmesg is still filled with:
> > 
> > read_tsc: ACK! TSC went backward! Unsynced TSCs?
> > 
> > Have you tried booting with idle=poll? I wonder if that would help?
> 
> No, I thought that was strictly an SMP issue. I'll try it as well.

It effects SMP mostly.  I doubt that it will effect UP, but the tsc is
still not consistent.

-- Steve


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