On Mon, Apr 25, 2016 at 02:12:09PM -0700, Vikas Shivappa wrote:
> >start: > > prev_count = read_hw_counter(); > > I am assuming this means we keep the prev_count when event is initialized. > This is done in the mbm_init which calls update_sample with first parameter > set to true.. No, when pmu::start() is called. > >read: > > do { > > prev = prev_count; > > cur_val = read_hw_counter(); > > delta = cur_val - prev; > > } while (local_cmpxchg(&prev_count, prev, cur_val) != prev); > > count += delta; And this you do on pmu::{stop,read}() > the update_sample does the work to compute the delta and add the delta to > total_bytes.. it has all the code except for the while loop. No, no, no, you add rc_count and st_count and generally make a huge mess of things. The above needs none of that. Because the above only cares about deltas against the hw counter (as per prev_count). Therefore count can be an absolute value that carries all your history as per rc_count, and you don't need st_count because per prev_count you don't care about the absolute value of the hw counter.