`On Fri, Mar 31, 2017 at 03:55:40AM -0700, Paul Turner wrote:> > I'm thinking that we can compute the middle segment, by taking the max> > value and chopping off the ends, like:> >> > >> >              p> >  c2 = 1024 \Sum y^n> >             n=1> >> >               inf        inf> >     = 1024 ( \Sum y^n - \Sum y^n - y^0 )> >               n=0        n=p> >> > Very nice!> Minor nit: Second sum needs to be from n=p+1Correct.> > +static u32 __accumulate_pelt_segments(u64 periods, u32 d1, u32 d3)> >  {> > +       u32 c1, c2, c3 = d3; /* y^0 == 1 */> >> >         /*> >          * c1 = d1 y^(p+1)> >          */> > +       c1 = decay_load((u64)d1, periods);> >> >         /*> > +        *             p> > +        * c2 = 1024 \Sum y^n> > +        *            n=1> >          *> > +        *              inf        inf> > +        *    = 1024 ( \Sum y^n - \Sum y^n - y^0 )> > +        *              n=0        n=p+1> >          */> > +       c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024;> > decay_load(LOAD_AVG_MAX, periods + 1)So here, @periods == p+1, see also c1. Yes, this is confusing [*].In particular, I think the decay terms for c1 and this should be thesame. We cut off this tail end of the series to replace it with c1 afterall.[*] hysterically p used to be off by 1, which is where the p+1 camefrom, but now periods includes it. I was thinking of doing a patchcorrecting all the comments to fully eradicate the whole +1 business.> I computed all the values vs true value that the old/new computations> result in, and it's very close.  Absolutely it's approximately 2x off> the previous computation, e.g. if the old value was -15 (relative to> true value) than the new computation is -30.> > This is definitely more than good enough.  If we want more precision,> then the correction factor of:>   +clamp(periods, 0, 45)Can you do a patch with coherent comment explaining where thatcorrection term comes from?`