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SubjectRe: [PATCH RFC V3 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once
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On Sat, 2015-08-29 at 07:32 -0700, Eric Dumazet wrote:
> On Sat, 2015-08-29 at 14:37 +0530, Raghavendra K T wrote:
>
> >
> > static inline void __snmp6_fill_stats64(u64 *stats, void __percpu *mib,
> > - int items, int bytes, size_t syncpoff)
> > + int items, int bytes, size_t syncpoff)
> > {
> > - int i;
> > + int i, c;
> > int pad = bytes - sizeof(u64) * items;
> > + u64 buff[items];
> > +
>
> One last comment : using variable length arrays is confusing for the
> reader, and sparse as well.
>
> $ make C=2 net/ipv6/addrconf.o
> ...
> CHECK net/ipv6/addrconf.c
> net/ipv6/addrconf.c:4733:18: warning: Variable length array is used.
> net/ipv6/addrconf.c:4737:25: error: cannot size expression
>
>
> I suggest you remove 'items' parameter and replace it by
> IPSTATS_MIB_MAX, as __snmp6_fill_stats64() is called exactly once.

If you respin, I suggest:

o remove "items" from the __snmp6_fill_stats64 arguments
and use IPSTATS_MIB_MAX in the function instead

o add braces around the for_each_possible_cpu loop

for_each_possible_cpu(c) {
for (i = 1; i < items; i++)
buff[i] += snmp_get_cpu_field64(mib, c, i, syncpoff);
}




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