From f0490980a152958d25ce9762bfb296d8fd4c5512 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <dada1@cosmosbay.com>
Date: Fri, 8 Dec 2006 00:08:43 -0800
Subject: [PATCH] [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>
---
include/linux/netdevice.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 631cec4ff5e1d..6be767c76b37d 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -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
*/
--
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