On Tue, 14 Jun 2016, Daniel Lezcano wrote: > On 06/10/2016 04:52 PM, Thomas Gleixner wrote: > > > > + timings->sum -= timings->values[timings->w_index]; > > > + timings->values[timings->w_index] = diff; > > > + timings->sum += diff; > > > > Now the real question is whether you really need all that math, checks and > > memsets in the irq hotpath. If you make the storage slightly larger then you > > can just store the values unconditionally in the circular buffer and do all > > the computational stuff when you really it. > > Yes, that was one concern when I wrote the code: do some basic computation > when an interrupt occurs, and the rest after or do the entire math when > entering idle. > > If the storage is a bit larger (let's say 16 values) and there is no memset > and the sum is not computed, at least we need a count for the number of values > in the array before this one is fulfilled, otherwise the statistics will be > wrong as we will take into account the entire array with old values, no ?
The point is not to change from 8 to 16 entries, but to store raw 64-bit timestamps instead of computed 32-bit deltas. Whether or not those timestamps are too far apart and discarded can be done at idle entry time. Nicolas
