Commit-ID: b247be3fe89b6aba928bf80f4453d1c4ba8d2063 Gitweb: https://git.kernel.org/tip/b247be3fe89b6aba928bf80f4453d1c4ba8d2063 Author: Will Deacon <[email protected]> AuthorDate: Thu, 26 Apr 2018 11:34:18 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 27 Apr 2018 09:48:47 +0200
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 <[email protected]> Signed-off-by: Will Deacon <[email protected]> Acked-by: Peter Zijlstra (Intel) <[email protected]> Acked-by: Waiman Long <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/include/asm/qspinlock.h | 2 ++ 1 file changed, 2 insertions(+) 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
