2019-07-15 19:28:00

by Alex Kogan

Subject: [PATCH v3 1/5] locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic

The arch_mcs_spin_unlock_contended macro should accept the value to be
stored into the lock argument as another argument. This allows using the
same macro in cases where the value to be stored is different from 1.

Signed-off-by: Alex Kogan <[email protected]>
Reviewed-by: Steve Sistare <[email protected]>
---
arch/arm/include/asm/mcs_spinlock.h | 4 ++--
kernel/locking/mcs_spinlock.h | 6 +++---
kernel/locking/qspinlock.c | 2 +-
3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/mcs_spinlock.h b/arch/arm/include/asm/mcs_spinlock.h
index 529d2cf4d06f..ae6d763477f4 100644
--- a/arch/arm/include/asm/mcs_spinlock.h
+++ b/arch/arm/include/asm/mcs_spinlock.h
@@ -14,9 +14,9 @@ do { \
wfe(); \
} while (0) \

-#define arch_mcs_spin_unlock_contended(lock) \
+#define arch_mcs_spin_unlock_contended(lock, val) \
do { \
- smp_store_release(lock, 1); \
+ smp_store_release(lock, (val)); \
dsb_sev(); \
} while (0)

diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index 5e10153b4d3c..bc6d3244e1af 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -41,8 +41,8 @@ do { \
* operations in the critical section has been completed before
* unlocking.
*/
-#define arch_mcs_spin_unlock_contended(l) \
- smp_store_release((l), 1)
+#define arch_mcs_spin_unlock_contended(l, val) \
+ smp_store_release((l), (val))
#endif

/*
@@ -115,7 +115,7 @@ void mcs_spin_unlock(struct mcs_spinlock **lock, struct mcs_spinlock *node)
}

/* Pass lock to next waiter. */
- arch_mcs_spin_unlock_contended(&next->locked);
+ arch_mcs_spin_unlock_contended(&next->locked, 1);
}

#endif /* __LINUX_MCS_SPINLOCK_H */
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index e14b32c69639..961781624638 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -558,7 +558,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
if (!next)
next = smp_cond_load_relaxed(&node->next, (VAL));

- arch_mcs_spin_unlock_contended(&next->locked);
+ arch_mcs_spin_unlock_contended(&next->locked, 1);
pv_kick_node(lock, next);

release:
--
2.11.0 (Apple Git-81)

2019-07-16 10:24:53

by Peter Zijlstra

Subject: Re: [PATCH v3 1/5] locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic

On Mon, Jul 15, 2019 at 03:25:32PM -0400, Alex Kogan wrote:

> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
> index e14b32c69639..961781624638 100644
> --- a/kernel/locking/qspinlock.c
> +++ b/kernel/locking/qspinlock.c
> @@ -558,7 +558,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
> if (!next)
> next = smp_cond_load_relaxed(&node->next, (VAL));
>
> - arch_mcs_spin_unlock_contended(&next->locked);
> + arch_mcs_spin_unlock_contended(&next->locked, 1);
> pv_kick_node(lock, next);

My problem with this patch is that the above reads really daft. Should
we rename the whole function? arch_mcs_pass_lock() perhaps?