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net: Rearrange dst_entry layout to avoid useless padding. 

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>
Reviewed-by: Eric Dumazet <edumazet@google.com>
This commit is contained in:
David Miller 2017-11-28 15:40:53 -05:00 committed by David S. Miller
parent 0f6c480f23
commit 8b207e7374
1 changed files with 12 additions and 19 deletions
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31
include/net/dst.h
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@ -34,7 +34,6 @@ 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;
@ -56,8 +55,6 @@ 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
@ -73,29 +70,25 @@ 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
*/
atomic_t __refcnt; /* client references */
#ifdef CONFIG_64BIT
atomic_t __refcnt; /* 64-bit offset 64 */
#endif
int __use;
unsigned long lastuse;
struct lwtunnel_state *lwtstate;
struct rcu_head rcu_head;
short error;
short __pad;
__u32 tclassid;
#ifndef CONFIG_64BIT
atomic_t __refcnt; /* 32-bit offset 64 */
#endif
union {
struct dst_entry *next;
};
@ -244,7 +237,7 @@ 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
* the placement of __refcnt in struct dst_entry
*/
BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63);
WARN_ON(atomic_inc_not_zero(&dst->__refcnt) == 0);