Valdis, Thanks a lot for you answer. this_cpu_sub() in fact is defined thus: # define this_cpu_sub(pcp, val) this_cpu_add((pcp), -(val))
so it does not matter so much. I did not know this_cpu_write() and it does work. Is __this_cpu_write() an atomic operation ? rgs Kevin On Sun, Apr 28, 2013 at 7:07 PM, <valdis.kletni...@vt.edu> wrote: > On Sat, 27 Apr 2013 19:34:00 +0300, Kevin Wilson said: >> Hello, > >> static int __init init_zeromib(void) > > This is your init routine... > >> { >> int ret = 0; >> printk("in %s\n",__func__); > > Missing KERN_DEBUG or similar here. This can cause it to fail > to appear in dmesg output, causing much confusion. > > >> #define SNMP_ZERO_STATS(mib, field) >> this_cpu_add(mib[0]->mibs[field],-(mib[0]->mibs[field])) > > You *do* realize that this doesn't in fact zero the statistics, right? > > If you have a 32-core machine, this will zero 1/32 of the statistics. > > this_cpu_add and friends are there specifically so that on multi-core systems > there's a lockless way to update the statistics values - to actually find > the values, you need to walk across all the per_cpu areas and sum them > up. > > And why for the love of all that is good did you do this bletcherous thing > with this_cpu_add() instead of using 'this_cpu_write(whatever, 0)'? Or at > least use this_cpu_sub()? ;) > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies