Messages in this thread |  | | | Date | Thu, 25 Sep 2008 19:07:19 -0700 | | From | Jeremy Fitzhardinge <> | | Subject | Re: [RFC PATCH 1/3] Unified trace buffer |
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Steven Rostedt wrote: > OK, let me rephrase my question. > > How and where do we record this? Do we keep this information in some > global variable that we must compare to every time we add a new item in > the trace? > > Do we have the buffer register a call back to record this information? >
Something like (total pseudocode):
struct tsc_time_parameters { int version; /* even - values OK; odd - values being updated */ u64 tsc; u32 tsc_freq; u64 gtod; }; DEFINE_PERCPU(struct tsc_time_parameters, tsc_params);
/* To be called after a tsc frequency change, before any new trace records are being emitted, in a context where we can call get_GTOD() */ void update_tsc_params(void) { struct tsc_time_parameters *p = __get_percpu_var(tsc_params); p->version |= 1; wmb(); p->tsc = get_tsc(); p->tsc_freq = get_tsc_freq(); p->gtod = get_GTOD();
wmb(); p->version++; wmb(); } DEFINE_PERCPU(unsigned, current_tsc_version); DEFINE_PERCPU(u64, prev_tsc);
/* may be called in any context */ u64 get_trace_timestamp_delta(void) { const struct tsc_time_parameters *p = &__get_percpu_var(tsc_params); unsigned *current_version = &__get_cpu_var(current_tsc_version); u64 prev = __get_cpu_var(prev_tsc); u64 now, ret; /* check the current tsc_params version against the last one we emitted; if the version is odd, then we interrupted the parameters as they were being updated, so just emit a new delta with the old parameters */ if (unlikely(*current_version != p->version && !(p->version & 1))) { /* XXX probably need a loop to deal with p->version changing under our feet */ emit_tsc_freq_record(p); prev = p->tsc; __get_cpu_var(current_tsc_version) = p->version; } now = read_tsc(); ret = now - prev; __get_cpu_var(prev_tsc) = now;
return ret; }
J
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