On 12/04/16 03:12, Yuyang Du wrote: > On Mon, Apr 11, 2016 at 11:41:28AM +0100, Juri Lelli wrote: > > Hi, > > > > On 11/04/16 06:36, Yuyang Du wrote: > > > __compute_runnable_contrib() uses a loop to compute sum, whereas a > > > table loopup can do it faster in a constant time. > > > > > > The following python script can be used to generate the constants: > > > > > > print " #: yN_inv yN_sum" > > > print "-----------------------" > > > y = (0.5)**(1/32.0) > > > x = 2**32 > > > xx = 1024 > > > for i in range(0, 32): > > > if i == 0: > > > x = x-1 > > > xx = xx*y > > > else: > > > x = x*y > > > xx = int(xx*y + 1024*y) > > > print "%2d: %#x %8d" % (i, int(x), int(xx)) > > > > > > print " #: sum_N32" > > > print "------------" > > > xxx = xx > > > for i in range(0, 11): > > > if i == 0: > > > xxx = xx > > > else: > > > xxx = xxx/2 + xx > > > print "%2d: %8d" % (i, xxx) > > > > > > > Thanks for the script, really useful. Do you think there is value in > > making it general? Like if we want to play with/need changing LOAD_AVG_ > > PERIOD in the future to something different than 32. > > i think a s/32/xx/ should work. > > > Also, does the following assume LOAD_AVG_PERIOD == 32? And if yes, do > > you think there is any value in removing that assumption? > > Like Peter said, we are heavily dependent on it already.
But I think the current code should still work if we define LOAD_AVG_ PERIOD as, say, 16 and we use Paul's program to recompute the tables. My point was about trying to keep everything related to LOAD_AVG_PERIOD and not start assuming it is 32. I'm not saying your changes assume that, I was asking if they do. > Whether a half-life > of 32 periods (or ~32ms) is the best, maybe we can try 16, but definitely not > 64. Or whether exponential decay is the best to compute the impact of old > runnable/running times as a pridiction, it is just I can't think of a better > approach yet, and credits to Paul, Ben, et al. > That is fine, I think. Another thing is crafting the code around a particular half-life, IMHO. Best, - Juri
