From: Christoph Lameter <christoph@xxxxxxxxxxx> Date: Thu, 23 Jun 2005 20:10:06 -0700 (PDT) > AIM7 results (tcp_test and udp_test) on i386 (IBM x445 8p 16G): > > No patch 94788.2 > w/patch 97739.2 (+3.11%) > > The numbers will be much higher on larger NUMA machines. How much higher? I don't believe it. And %3 doesn't justify the complexity (both in time and memory usage) added by this patch. Performance of our stack's routing cache is _DEEPLY_ tied to the size of the routing cache entries, of which dst entry is a member. Every single byte counts. You've exploded this to be (NR_NODES * sizeof(void *)) larger. That is totally unacceptable, even for NUMA. Secondly, inlining the "for_each_online_node()" loops isn't very nice either. Consider making a per-node routing cache instead, just like the flow cache is per-cpu, or make socket dst entries have a per-node array of object pointers. Fill the per-node array in lazily, just as you do for the dst. The first time you try to clone a dst on a cpu for a socket, create the per-cpu entry slot. We don't need to make them per-node system wide, only per-socket is this really needed. This way you do per-node walking when you detach the dst from the socket at close() time, not at every dst_release() call, and thus for every packet in the system. In light of that, I don't see what the advantage is. Instead of atomic inc/dec on every packet sent in the system, you walk the whole array of counters for every packet sent in the system. If you really get contention amongst nodes for a DST entry, this walk should result in ReadToShare transactions, and thus cacheline movement, between the NUMA nodes, on every __kfree_skb() call. Essentially you're trading 1 atomic inc (ReadToOwn) and 1 atomic dec (ReadToOwn) per packet for significant extra memory, much bigger code, and 1 ReadToShare transaction per packet. And since you're still using atomic_inc/atomic_dec you'll still hit ReadToOwn transactions within the node. - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
