Re: [PATCH RFC V3 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once

[Raghavendra K T]

On 08/29/2015 08:51 PM, Joe Perches wrote:
> 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

Yes, as also suggested by Eric.

> 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);
> 	}

Sure. It makes it more readable.
will respin V4 with these changes (+ memset 0 for pad which I realized).



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