[RFC v2 PATCH 09/11] net: Rearrange dst_entry layout to avoid useless padding.
From: "David S. Miller" <davem@davemloft.net>
Date: 2017-10-31 14:20:38
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
We have padding to try and align the refcount on a separate cache line. But after several simplifications the padding has increased substantially. So now it's easy to change the layout to get rid of the padding entirely. We group the write-heavy __refcnt and __use with less often used items such as the rcu_head and the error code. Signed-off-by: David S. Miller <davem@davemloft.net> --- include/net/dst.h | 22 +++++----------------- 1 file changed, 5 insertions(+), 17 deletions(-)
diff --git a/include/net/dst.h b/include/net/dst.h
index e860c3b11322..ffd0d81f861f 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h@@ -33,7 +33,6 @@ struct sk_buff; struct dst_entry { struct net_device *dev; - struct rcu_head rcu_head; struct dst_ops *ops; unsigned long _metrics; unsigned long expires;
@@ -55,8 +54,6 @@ struct dst_entry { #define DST_XFRM_QUEUE 0x0040 #define DST_METADATA 0x0080 - short error; - /* A non-zero value of dst->obsolete forces by-hand validation * of the route entry. Positive values are set by the generic * dst layer to indicate that the entry has been forcefully
@@ -72,21 +69,7 @@ struct dst_entry { #define DST_OBSOLETE_KILL -2 unsigned short header_len; /* more space at head required */ unsigned short trailer_len; /* space to reserve at tail */ - unsigned short __pad3; - -#ifdef CONFIG_IP_ROUTE_CLASSID - __u32 tclassid; -#else - __u32 __pad2; -#endif -#ifdef CONFIG_64BIT - /* - * Align __refcnt to a 64 bytes alignment - * (L1_CACHE_SIZE would be too much) - */ - long __pad_to_align_refcnt[5]; -#endif /* * __refcnt wants to be on a different cache line from * input/output/ops or performance tanks badly
@@ -95,6 +78,11 @@ struct dst_entry { int __use; unsigned long lastuse; struct lwtunnel_state *lwtstate; + struct rcu_head rcu_head; + short error; + short __pad; + __u32 tclassid; + union { struct dst_entry *next; };
--
2.13.6