diff options
| author | Will Deacon <will.deacon@arm.com> | 2018-12-18 18:13:59 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-12-21 14:13:09 +0100 |
| commit | 4e21502d37a503d4311e2bdb46a66aef783a7cfe (patch) | |
| tree | f0c6894424ef04cc175f4d11ae559b73a44564ca /kernel/locking/qspinlock.c | |
| parent | 49849a651b8456263391ae767be6f7d02af8ef26 (diff) | |
locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound
commit b247be3fe89b6aba928bf80f4453d1c4ba8d2063 upstream.
On x86, atomic_cond_read_relaxed will busy-wait with a cpu_relax() loop,
so it is desirable to increase the number of times we spin on the qspinlock
lockword when it is found to be transitioning from pending to locked.
According to Waiman Long:
| Ideally, the spinning times should be at least a few times the typical
| cacheline load time from memory which I think can be down to 100ns or
| so for each cacheline load with the newest systems or up to several
| hundreds ns for older systems.
which in his benchmarking corresponded to 512 iterations.
Suggested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-5-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel/locking/qspinlock.c')
0 files changed, 0 insertions, 0 deletions