[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>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 631cec4..6be767c 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -193,7 +193,14 @@
{
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
*/