Re: [PATCH] Add prefetches in net/ipv4/route.c

[Robert Olsson <Robert.Olsson@xxxxxxxxxxx>]

Eric Dumazet writes:

 > I have no profiling info for this exact patch, I'm sorry David.
 > On a dual opteron machine, this thing from ip_route_input() is very 
 > expensive :
 > 
 >   RT_CACHE_STAT_INC(in_hlist_search);
 > 
 > ip_route_input() use a total of 3.4563 % of one cpu, but this 'increment' 
 > takes 1.20 % !!!

 Very weird if the statscounter taking a third of ip_route_input.

 > Sometime I wonder if oprofile can be trusted :(
 > 
 > Maybe we should increment a counter on the stack and do a final
 >     if (counter != 0)
 >         RT_CACHE_STAT_ADD(in_hlist_search, counter);

 My experiences from playing with prefetching eth_type_trans in this 
 case. One must look in the total performance not just were the 
 prefetching is done. In this case I was able to get eth_type_trans
 down in the profile list but other functions increased so performance
 was the same or lower. This needs to be sorted out... 

 Cheers.
                                        --ro