Messages in this thread | | | Date | Tue, 01 Mar 2011 09:45:27 -0700 | From | David Ahern <> | Subject | Re: [PATCH 3/6] perf record: add time-of-day option |
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On 03/01/2011 09:37 AM, Peter Zijlstra wrote: > On Tue, 2011-03-01 at 09:09 -0700, David Ahern wrote: >> >> I did not code it create samples of a realtime-clock event; I coded it >> to add an event to the stream on demand -- whatever event the fd is >> tied to. >> >> > Well yes, but aside from you and the realtime clock stuff, who'd ever > want to do this particular thing?
One example would be a system watchdog that decided for some reason or another to force an event sample because of some event it detected.
> > I'd much rather expose the whole > local_clock()/perf_clock()/trace_clock() (should all be the same anyway) > as a posix clock using CLOCK_TRACING or whatever would be an appropriate > name. > > [ Since the whole thing is NMI safe it should be well possible to make a > VDSO version as well. ] > > Anyway, once its visible as a posix clock you can sync up from > userspace. And this clock is indeed wanted for other things too, like > user-space tracing etc. >
And for some silly reason I sense a time trap here (pun intended) .....
So your pushback is: 1. throw out the realtime-clock event patch,
2. add a new CLOCK_TRACING type to clock_gettime with VDSO hook,
3. and use a synthesized event from userspace for snapshotting perf_clock to time-of-day -- similar to what I have now, but one that will guarantee a time-of-day to perf_clock correlation (versus the current one which hopes that perf_clock is the monotonic clock).
David
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