path: root/net/ipv4/Kconfig
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authorEric Dumazet <eric.dumazet@gmail.com>2010-10-03 22:17:54 -0700
committerDavid S. Miller <davem@davemloft.net>2010-10-03 22:17:54 -0700
commitc7d4426a98a5f6654cd0b4b33d9dab2e77192c18 (patch)
tree0db2524e6f3f742861765dd6aa696a9271767056 /net/ipv4/Kconfig
parentsctp: Fix break indentation in sctp_ioctl(). (diff)
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 <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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