Messages in this thread | | | Date | Tue, 3 May 2016 09:46:50 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/4] perf/x86/mbm: Store bytes counted for mbm during recycle |
| |
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.
| |