* Abbas Raza ([email protected]) wrote: > On 07/26/2011 10:17 PM, Mathieu Desnoyers wrote: >> * Abbas Raza ([email protected]) wrote: >> [...] >>> Hi Mathieu, >>> >>> Some confusion here :( >>> >>> In case of LTTng 0.x, when we take kernel traces then timestamps for >>> these traces is based on TSC/TB . So after that we view these traces by >>> lttv and it shows timestamps with all events which occurred. >>> I print the timestamp in kernel ltt function 'ltt_trace_alloc()' and it >>> comes out to be 22944596907 (by calling trace_clock_read64() ). While >>> lttv show Birth sec of first event to 367 second. How this conversion is >>> made from TSC to the Birth sec/nsec value displayed in lttv? just want >>> to confirm that whether timestamps shown in lttv (Birth sec/nsec) are >>> based on TSC values... if yes then how TSC values are converted to Birth >>> sec/nsec and i no then from where lttv gets timestamps to be displayed? >>> Or in simple words, do kernel traces which we get contain timestamps >>> based simply on TSC values or it is something else? >> Yes, we write, in the lttng 0.x headers, the following information: >> >> struct ltt_subbuffer_header { >> [...] >> uint64_t start_freq; /* >> * Frequency at trace start, >> * used all along the trace. >> */ >> uint32_t freq_scale; /* Frequency scaling (divisor) */ >> [...] >> } >> >> so by using the start frequency and the scale, we can convert from TSC >> values to nanoseconds. Please note that LTTng 0.x requires the clock >> source to appear as if it has a constant rate. >> >> These values map to trace_clock_frequency() and trace_clock_freq_scale() >> trace clock functions. >> >> Best regards, >> >> Mathieu >> >>> Thanks a lot again for help :) >>> >>> >>> Abbas Raza >>> > > Just to confirm that TSC's just have raw values of clock cycles and lttv > converts these values into sec/nsec by reading ltt_subbuffer_header ?
Yes, that's it. Thanks, Mathieu > > > Thanks! > > Abbas Raza > -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com _______________________________________________ ltt-dev mailing list [email protected] http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
