diff options
| author | Will Deacon <will.deacon@arm.com> | 2018-04-26 11:34:18 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-04-27 09:48:47 +0200 |
| commit | b247be3fe89b6aba928bf80f4453d1c4ba8d2063 (patch) | |
| tree | 4e3ca1be09b40d6885eae9a2d2a432afb7cfeb30 | |
| parent | 6512276d97b160d90b53285bd06f7f201459a7e3 (diff) | |
locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound
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>
| -rw-r--r-- | arch/x86/include/asm/qspinlock.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 90b0b0ed8161..da1370ad206d 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -7,6 +7,8 @@ #include <asm-generic/qspinlock_types.h> #include <asm/paravirt.h> +#define _Q_PENDING_LOOPS (1 << 9) + #define queued_spin_unlock queued_spin_unlock /** * queued_spin_unlock - release a queued spinlock |