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| author | Mark Rutland <mark.rutland@arm.com> | 2018-06-21 13:13:06 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-06-21 14:22:33 +0200 |
| commit | f74445b6dd6b8f33ed34e005d19ecbb49171dabf (patch) | |
| tree | 5e12a311221be0cd9bd0e34ae0f910b56cc5a116 /net/atm | |
| parent | 8b47038e6d349cca950e75076566a0de990c4645 (diff) | |
| download | linux-f74445b6dd6b8f33ed34e005d19ecbb49171dabf.tar.gz linux-f74445b6dd6b8f33ed34e005d19ecbb49171dabf.tar.bz2 linux-f74445b6dd6b8f33ed34e005d19ecbb49171dabf.zip | |
atomics/treewide: Remove atomic_inc_not_zero_hint()
While documentation suggests atomic_inc_not_zero_hint() will perform better
than atomic_inc_not_zero(), this is unlikely to be the case. No architectures
implement atomic_inc_not_zero_hint() directly, and thus it either falls back to
atomic_inc_not_zero(), or a loop using atomic_cmpxchg().
Whenever the hint does not match the value in memory, the repeated use of
atomic_cmpxchg() will be more expensive than the read that
atomic_inc_not_zero_hint() attempts to avoid. For architectures with LL/SC
atomics, a read cannot be avoided, and it would always be better to use
atomic_inc_not_zero() directly. For other architectures, their own
atomic_inc_not_zero() is likely to be more optimal than an atomic_cmpxchg()
loop regardless.
Generally, atomic_inc_not_zero_hint() is liable to perform worse than
atomic_inc_not_zero(). Further, atomic_inc_not_zero_hint() only exists
for atomic_t, and not atomic64_t or atomic_long_t, and there is only one
user in the kernel tree.
Given all this, let's remove atomic_inc_not_zero_hint(), and migrate the
existing user over to atomic_inc_not_zero().
There should be no functional change as a result of this patch.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/20180621121321.4761-4-mark.rutland@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'net/atm')
| -rw-r--r-- | net/atm/pppoatm.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/atm/pppoatm.c b/net/atm/pppoatm.c index af8c4b38b746..d84227d75717 100644 --- a/net/atm/pppoatm.c +++ b/net/atm/pppoatm.c @@ -244,7 +244,7 @@ static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size) * the packet count limit, so... */ if (atm_may_send(pvcc->atmvcc, size) && - atomic_inc_not_zero_hint(&pvcc->inflight, NONE_INFLIGHT)) + atomic_inc_not_zero(&pvcc->inflight)) return 1; /* |