From c7d4426a98a5f6654cd0b4b33d9dab2e77192c18 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 3 Oct 2010 22:17:54 -0700 Subject: net: introduce DST_NOCACHE flag While doing stress tests with IP route cache disabled, and multi queue devices, I noticed a very high contention on one rwlock used in neighbour code. When many cpus are trying to send frames (possibly using a high performance multiqueue device) to the same neighbour, they fight for the neigh->lock rwlock in order to call neigh_hh_init(), and fight on hh->hh_refcnt (a pair of atomic_inc/atomic_dec_and_test()) But we dont need to call neigh_hh_init() for dst that are used only once. It costs four atomic operations at least, on two contended cache lines, plus the high contention on neigh->lock rwlock. Introduce a new dst flag, DST_NOCACHE, that is set when dst was not inserted in route cache. With the stress test bench, sending 160000000 frames on one neighbour, results are : Before patch: real 2m28.406s user 0m11.781s sys 36m17.964s After patch: real 1m26.532s user 0m12.185s sys 20m3.903s Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/dst.h | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) (limited to 'include/net/dst.h') diff --git a/include/net/dst.h b/include/net/dst.h index aa53fbc34b2b..a217c838ec0d 100644 --- a/include/net/dst.h +++ b/include/net/dst.h @@ -43,10 +43,11 @@ struct dst_entry { short error; short obsolete; int flags; -#define DST_HOST 1 -#define DST_NOXFRM 2 -#define DST_NOPOLICY 4 -#define DST_NOHASH 8 +#define DST_HOST 0x0001 +#define DST_NOXFRM 0x0002 +#define DST_NOPOLICY 0x0004 +#define DST_NOHASH 0x0008 +#define DST_NOCACHE 0x0010 unsigned long expires; unsigned short header_len; /* more space at head required */ -- cgit v1.2.3