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fib: introduce fib_alias_accessed() helper

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Perf tools session at NFWS 2010 pointed out a false sharing on struct
fib_alias that can be avoided pretty easily, if we set FA_S_ACCESSED bit
only if needed (ie : not already set)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2010-10-20 22:03:38 +00:00 committed by David S. Miller
parent 7b5edbc4cf
commit 9b0c290e78
4 changed files with 12 additions and 3 deletions
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3
net/ipv4/fib_hash.c
View file

@ -335,7 +335,8 @@ void fib_table_select_default(struct fib_table *tb,
if (!next_fi->fib_nh[0].nh_gw ||
next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK)
continue;
fa->fa_state |= FA_S_ACCESSED;
fib_alias_accessed(fa);
if (fi == NULL) {
if (next_fi != res->fi)

7
net/ipv4/fib_lookup.h
View file

@ -17,6 +17,13 @@ struct fib_alias {
#define FA_S_ACCESSED 0x01
/* Dont write on fa_state unless needed, to keep it shared on all cpus */
static inline void fib_alias_accessed(struct fib_alias *fa)
{
if (!(fa->fa_state & FA_S_ACCESSED))
fa->fa_state |= FA_S_ACCESSED;
}
/* Exported by fib_semantics.c */
extern int fib_semantic_match(struct list_head *head,
const struct flowi *flp,

2
net/ipv4/fib_semantics.c
View file

@ -901,7 +901,7 @@ int fib_semantic_match(struct list_head *head, const struct flowi *flp,
if (fa->fa_scope < flp->fl4_scope)
continue;
fa->fa_state |= FA_S_ACCESSED;
fib_alias_accessed(fa);
err = fib_props[fa->fa_type].error;
if (err == 0) {

3
net/ipv4/fib_trie.c
View file

@ -1838,7 +1838,8 @@ void fib_table_select_default(struct fib_table *tb,
if (!next_fi->fib_nh[0].nh_gw ||
next_fi->fib_nh[0].nh_scope != RT_SCOPE_LINK)
continue;
fa->fa_state |= FA_S_ACCESSED;
fib_alias_accessed(fa);
if (fi == NULL) {
if (next_fi != res->fi)