From 5635c10d976716ef47ae441998aeae144c7e7387 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 16 Nov 2008 19:46:36 -0800 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- include/net/dst.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) 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); } -- 2.30.2