On Tue, 2011-03-01 at 09:45 -0700, David Ahern wrote: > 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. That would be a design error, there already is an event, use that. > > > > 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, Well, no, you need continues samples to keep in sync, so having this is required [*]. > 2. add a new CLOCK_TRACING type to clock_gettime with VDSO hook, Right, that is something we need anyway at some point in time. > 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). I guess you could do that if we have full userspace tracing support, but it wouldn't need synthesized events, it would need a pure userspace event stream. Thing is, I really dislike the ioctl() trigger -- To unsubscribe from this list: send the line "unsubscribe linux-perf-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html