`On Fri, Mar 31, 2017 at 03:13:55AM +0800, Yuyang Du wrote:> On Thu, Mar 30, 2017 at 04:14:28PM +0200, Peter Zijlstra wrote:> > On Thu, Mar 30, 2017 at 02:16:58PM +0200, Peter Zijlstra wrote:> > > On Thu, Mar 30, 2017 at 04:21:08AM -0700, Paul Turner wrote:> > > > > > > +> > > > > +       if (unlikely(periods >= LOAD_AVG_MAX_N))> > > > >                 return LOAD_AVG_MAX;> > > > > > > > > > Is this correct in the iterated periods > LOAD_AVG_MAX_N case?> > > > I don't think the decay above is guaranteed to return these to zero.> > > > > > Ah!> > > > > > Indeed, so decay_load() needs LOAD_AVG_PERIOD * 63 before it truncates> > > to 0, because every LOAD_AVG_PERIOD we half the value; loose 1 bit; so> > > 63 of those and we're 0.> > > > > > But __accumulate_sum() OTOH returns LOAD_AVG_MAX after only> > > LOAD_AVG_MAX_N, which < LOAD_AVG_PERIOD * 63.> > > > > > So yes, combined we exceed LOAD_AVG_MAX, which is bad. Let me think what> > > to do about that.> > > > > > So at the very least it should be decay_load(LOAD_AVG_MAX, 1) (aka> > LOAD_AVG_MAX - 1024), but that still doesn't account for the !0> > decay_load() of the first segment.> > > > 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> > It looks surprisingly kinda works :)> > > +	c2 = LOAD_AVG_MAX - decay_load(LOAD_AVG_MAX, periods) - 1024;>                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~> But, I'm not sure               this is what you want (just assume p==0).> Oh, what I meant is when p != 0, actually p>=1.And thinking about it for a while, it's really what you want, brilliant :)`