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.Kletnieks@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()? ;)