Re: [PATCH V4] irq: Track the interrupt timings

[Daniel Lezcano]

On 06/14/2016 05:10 PM, Nicolas Pitre wrote:
> 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.

Ah, ok. That makes sense.

Thanks for the clarification.

 -- Daniel

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