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net: updating dst lastusage is an unlikely event.

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Since commit 0da4af00b2ed ("ipv6: only update __use and lastusetime
once per jiffy at most"), updating the dst lastuse field is an
unlikely action: it happens at most once per jiffy, out of
potentially millions of calls per second.

Mark explicitly the code as such, and let the compiler generate
better code.

Note: gcc 7.2 and several older versions do actually generate
different - better - code when the unlikely() hint is in place,
avoid jump in the fast path and keeping better code locality.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2017-10-24 12:41:01 +02:00 committed by David S. Miller
parent a4484705b1
commit 32d18ab1d4
1 changed files with 1 additions and 1 deletions
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2
include/net/dst.h
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@ -257,7 +257,7 @@ static inline void dst_hold(struct dst_entry *dst)
static inline void dst_use_noref(struct dst_entry *dst, unsigned long time)
{
if (time != dst->lastuse) {
if (unlikely(time != dst->lastuse)) {
dst->__use++;
dst->lastuse = time;
}