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[NET]: Force a cache line split in hh_cache in SMP. 

hh_lock was converted from rwlock to seqlock by Stephen.

To have a 100% benefit of this change, I suggest to place read mostly fields
of hh_cache in a separate cache line, because hh_refcnt may be changed quite
frequently on some busy machines.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2006-12-08 00:08:43 -08:00 committed by David S. Miller
parent 47bbec0282
commit f0490980a1
1 changed files with 8 additions and 1 deletions
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9
include/linux/netdevice.h
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@ -193,7 +193,14 @@ struct hh_cache
{
struct hh_cache *hh_next; /* Next entry */
atomic_t hh_refcnt; /* number of users */
__be16 hh_type; /* protocol identifier, f.e ETH_P_IP
/*
* We want hh_output, hh_len, hh_lock and hh_data be a in a separate
* cache line on SMP.
* They are mostly read, but hh_refcnt may be changed quite frequently,
* incurring cache line ping pongs.
*/
__be16 hh_type ____cacheline_aligned_in_smp;
/* protocol identifier, f.e ETH_P_IP
* NOTE: For VLANs, this will be the
* encapuslated type. --BLG
*/