Messages in this thread | | | Date | Mon, 22 Sep 2008 16:16:41 -0700 | From | "Martin Bligh" <> | Subject | Re: Unified tracing buffer |
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>> One thing that I think is still important is to have a unified timestamp >> mechanism on everything, so we can co-ordinate different things back >> together in userspace from different trace tools, so I intend to keep >> that at a lower level, but I think you're right that the event id, etc can >> move up into separate layers. > > I'm not so sure that the unified 'timestamp' must be required by all tracers. > If you just need to merge and sort per-cpu data, you can use an atomic > sequential number for it. > IMHO, the unified 'timestamp' would better be an option, because some > architectures can't support it. I think preparing timestamp-callback > function will help us.
An atomic sequential number is:
(a) far less meaningful than a timestamp for the user (b) more expensive to compute in many cases.
I think we came up with a way to approximate this, using a callback every ms or so as the higher order bits, and a sequential counter in the lower order for those broken platforms.
But perhaps it would be better if we started with a discussion of which platforms can't do global timestamps, and why not? I know some of them are fixable, but perhaps not all.
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