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| author | Eric Dumazet <dada1@cosmosbay.com> | 2008-11-17 04:46:36 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2008-11-17 04:46:36 +0100 |
| commit | 5635c10d976716ef47ae441998aeae144c7e7387 (patch) | |
| tree | 03cb08b634fba283bbde42ea290c92048045d2fd /include/net/dst.h | |
| parent | rcu: documents rculist_nulls (diff) | |
| download | linux-5635c10d976716ef47ae441998aeae144c7e7387.tar.xz linux-5635c10d976716ef47ae441998aeae144c7e7387.zip | |
net: make sure struct dst_entry refcount is aligned on 64 bytes
As found in the past (commit f1dd9c379cac7d5a76259e7dffcd5f8edc697d17
[NET]: Fix tbench regression in 2.6.25-rc1), it is really
important that struct dst_entry refcount is aligned on a cache line.
We cannot use __atribute((aligned)), so manually pad the structure
for 32 and 64 bit arches.
for 32bit : offsetof(truct dst_entry, __refcnt) is 0x80
for 64bit : offsetof(truct dst_entry, __refcnt) is 0xc0
As it is not possible to guess at compile time cache line size,
we use a generic value of 64 bytes, that satisfies many current arches.
(Using 128 bytes alignment on 64bit arches would waste 64 bytes)
Add a BUILD_BUG_ON to catch future updates to "struct dst_entry" dont
break this alignment.
"tbench 8" is 4.4 % faster on a dual quad core (HP BL460c G1), Intel E5450 @3.00GHz
(2350 MB/s instead of 2250 MB/s)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net/dst.h')
| -rw-r--r-- | include/net/dst.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/include/net/dst.h b/include/net/dst.h index 65a60fab2f82..6c778799bf10 100644 --- a/include/net/dst.h +++ b/include/net/dst.h @@ -61,6 +61,8 @@ struct dst_entry struct hh_cache *hh; #ifdef CONFIG_XFRM struct xfrm_state *xfrm; +#else + void *__pad1; #endif int (*input)(struct sk_buff*); int (*output)(struct sk_buff*); @@ -71,8 +73,20 @@ struct dst_entry #ifdef CONFIG_NET_CLS_ROUTE __u32 tclassid; +#else + __u32 __pad2; #endif + + /* + * Align __refcnt to a 64 bytes alignment + * (L1_CACHE_SIZE would be too much) + */ +#ifdef CONFIG_64BIT + long __pad_to_align_refcnt[2]; +#else + long __pad_to_align_refcnt[1]; +#endif /* * __refcnt wants to be on a different cache line from * input/output/ops or performance tanks badly @@ -157,6 +171,11 @@ dst_metric_locked(struct dst_entry *dst, int metric) static inline void dst_hold(struct dst_entry * dst) { + /* + * If your kernel compilation stops here, please check + * __pad_to_align_refcnt declaration in struct dst_entry + */ + BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63); atomic_inc(&dst->__refcnt); } |