2014-09-26 (금), 11:58 +0100, Pawel Moll: > On Fri, 2014-09-26 at 07:16 +0100, Namhyung Kim wrote: > > > It would be doable, I guess, but what > > > if someone *wants* to have sched clock as the timestamps source (because > > > it's cheap) but still be able to correlate them with userspace? In this > > > case two separate timestamps are required to do the approximation. > > > > But by collecting two timestamps, you'll loose the win of the first > > timestamp, no? > > But I can ask for both timestamps only being collected on "low > bandwidth" events, in particular context switches and/or periodic (eg. > 10ms hrtimer) software events. > > Then I have loads of normal normal samples, timestamped with sched clock > only, and every now and then one with both timestamps which then I can > use for time correlation. The whole point is that the frequency of such > "synchronisation" event can be much (much!) lower than of the normal > samples, but it still allows pretty good approximation (I was getting > accuracy of ~1 microsecond and better with sched_switch trace event > marked with additional raw monotonic timestamp).
Okay. But in that case wouldn't it be enough to use just a single timestamp for each event - sched_clock for cpu-cycles and monotonic raw for sched_switch? > > Pawel > > PS. Have you sent a couple of the messages via some kind of gmane's > proxy? All the mail addresses got rather messed up... > Yes, I use gnus to communicate with lkml, but it seems it messed up mail addresses if it contains some list (like linux-api ?). Sorry about that. Thanks, Namhyung -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
