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Date: Tue, 23 Sep 2008 14:02:08 -0700
From: "Martin Bligh" <mbligh@google.com>
To: "Thomas Gleixner" <tglx@linutronix.de>
Subject: Re: Unified tracing buffer
Cc: "Masami Hiramatsu" <mhiramat@redhat.com>,
       "Linus Torvalds" <torvalds@linux-foundation.org>,
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>> I think the tolerance is about 500 cycles. If that's not sufficient, I guess
>> we'll have to either live with some slight misordering (which people have
>> pointed out is kind of inevitable anyway) on these broken machines?
>> It was sufficient for what we were using it for, but maybe not for everyone.
>
> Well, I dont care about the trace reordering at all. I care about user
> space visible time going backwards issues observed via the
> gettimeofday vsyscall. 500 cycles should be fine, I doubt that we can
> migrate in less than that :)

Right, that's what we were interested in.

> I guess you try this only for machines where the TSC runs with
> constant frequency, right ?

We don't do DVFS on the 'broken' TSC machines, just halt.
But yes, it's selective