From: Eric Dumazet <[EMAIL PROTECTED]> Date: Wed, 7 Feb 2007 11:59:34 +0100
> ehash table layout is currently this one : > > First half of this table is used by sockets not in TIME_WAIT state > Second half of it is used by sockets in TIME_WAIT state. > > This is non optimal because of for a given hash or socket, the two chain > heads > are located in separate cache lines. > Moreover the locks of the second half are never used. > > If instead of this halving, we use two list heads in inet_ehash_bucket > instead > of only one, we probably can avoid one cache miss, and reduce ram usage, > particularly if sizeof(rwlock_t) is big (various CONFIG_DEBUG_SPINLOCK, > CONFIG_DEBUG_LOCK_ALLOC settings). So we still halves the table but we keep > together related chains to speedup lookups and socket state change. > > In this patch I did not try to align struct inet_ehash_bucket, but a future > patch could try to make this structure have a convenient size (a power of two > or a multiple of L1_CACHE_SIZE). > I guess rwlock will just vanish as soon as RCU is plugged into ehash :) , so > maybe we dont need to scratch our heads to align the bucket... > > Note : In case struct inet_ehash_bucket is not a power of two, we could > probably change alloc_large_system_hash() (in case it use __get_free_pages()) > to free the unused space. It currently allocates a big zone, but the last > quarter of it could be freed. Again, this should be a temporary 'problem'. > > Patch tested on ipv4 tcp only, but should be OK for IPV6 and DCCP. > > Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]> I've applied this, but I _REALLY_ don't like the new multiply instructions that are used now in the hash indexing paths when CONFIG_SMP is set. I think that's a higher cost than the memory waste. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
