Messages in this thread | | | Date | Wed, 2 Mar 2011 18:28:18 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH 3/6] perf record: add time-of-day option |
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On Wed, 2 Mar 2011, David Ahern wrote: > On 03/02/2011 07:16 AM, Thomas Gleixner wrote: > > How does all that deal with CLOCK_REALTIME being affected by NTP and > > settimeofday? Not really, as far as I can tell. It somehow works, but > > that depends on the frequency of your event injection. > > It is sampled at some periodic rate to get NTP changes. Right now it is > hardcoded at once an hour. The frequency option can be added to the > --tod parameter.
Once an hour. Brilliant. And how do you correlated that when settimeofday was called 5 times in between the samples. Not at all.
> > > > To be honest, that's just too much churn for a feature which is single > > purpose and questionable functionality. > > > > It would be far more interesting to have trace points in the > > timekeeping code, which are useful for other things as well > > (e.g. precise monitoring of NTP) and provide always a correct > > association with the trace clock. That would cover everything from > > frequency adjustments, clock setting including the information about > > the relation to clock monotonic. > > I'm not looking to track ntp changes. I want time-of-day strings on > sample dumps. That is not a questionable feature request; it is a > usability enhancement.
Sigh, did you even read what I wrote?
I did not say, that YOU have to track NTP changes.
And I fully understood that you want to correlate perf time stamps with CLOCK_REALTIME.
Neither did I say, that this is a questionable feature request.
I merily objected to add functionality which is half baken and only particular useful.
Further I made a suggestion to add trace points to the time keeping code instead, which
- solve your problem - are useful for other purposes - do not require ioctls, timer driven sw events
Thanks,
tglx
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