`Le lundi 30 janvier 2012 à 09:06 +0100, Jörg-Volker Peetz a écrit :> Eric Dumazet wrote, on 01/25/12 01:26:> > Le mercredi 25 janvier 2012 à 09:18 +0900, KAMEZAWA Hiroyuki a écrit :> > > >> BTW, what is the reason of this change ?> >>> >>> -	unsigned size = 4096 * (1 + num_possible_cpus() / 32);> >>> +	unsigned size = 1024 + 128 * num_possible_cpus();> >>> >> I think size of buffer is affected by the number of online cpus.> >> (Maybe 128 is enough but please add comment why 128 ?)> >>> > > > There is no change, as 4096/32 is 128 bytes per cpu.> > > > Wrong math, only num_possible_cpus() is divided by 32. Thus,> > -	unsigned size = 4096 * (1 + num_possible_cpus() / 32);> +	unsigned size = 4096 + 128 * num_possible_cpus();> > <snip>It is good math, once you take the time to think a bit about it.The original question was about the 128 * num_possible_cpus()4096/32 is 128 as I said. The 4096 -> 1024 is just taking into account fact that once you do thecorrect computations, you dont need initial 4096 value, and 1024 is morethan enough.Example on a dual core machine : # dmesg|grep nr_irq[    0.000000] nr_irqs_gsi: 40[    0.000000] NR_IRQS:2304 nr_irqs:712 16size = 1024 + 2*128 + 2*712 = 2704 bytes (rounded to 4096 by kmalloc())# wc -c /proc/stat1767 /proc/statProblem with original math was that for a machine with 16 cpus or amachine with 1 cpu, we ended with the same 4096 value. That was a realproblem.If we instead use "unsigned size = 4096 + 128 * num_possible_cpus();" asyou suggest, we would always allocate 2 pages of memory, this is notneeded at all for typical 1/2/4 way machines.--To unsubscribe from this list: send the line "unsubscribe linux-kernel" inthe body of a message to majordomo@vger.kernel.orgMore majordomo info at  http://vger.kernel.org/majordomo-info.htmlPlease read the FAQ at  http://www.tux.org/lkml/`