Use !try_cmpxchg() instead of cmpxchg (*ptr, old, new) != old.
x86 CMPXCHG instruction returns success in ZF flag, so this
change saves a compare after CMPXCHG.
The generated assembly code improves from e.g.:
415: 48 8b 44 24 30 mov 0x30(%rsp),%rax
41a: 48 8b 54 24 38 mov 0x38(%rsp),%rdx
41f: f0 49 0f b1 91 a8 02 lock cmpxchg %rdx,0x2a8(%r9)
426: 00 00
428: 48 3b 44 24 30 cmp 0x30(%rsp),%rax
42d: 0f 84 09 ff ff ff je 33c <...>
to:
415: 48 8b 44 24 30 mov 0x30(%rsp),%rax
41a: 48 8b 54 24 38 mov 0x38(%rsp),%rdx
41f: f0 49 0f b1 91 a8 02 lock cmpxchg %rdx,0x2a8(%r9)
426: 00 00
428: 0f 84 0e ff ff ff je 33c <...>
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Cc: "K. Y. Srinivasan" <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Wei Liu <[email protected]>
Cc: Dexuan Cui <[email protected]>
Cc: Long Li <[email protected]>
---
drivers/hv/hyperv_vmbus.h | 4 ++--
drivers/hv/mshv_eventfd.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index cdbc5f5c3215..7bd8f8486e85 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -370,8 +370,8 @@ static inline void vmbus_signal_eom(struct hv_message *msg,
u32 old_msg_type)
* CHANNELMSG_UNLOAD_RESPONSE and we don't care about other messages
* on crash.
*/
- if (cmpxchg(&msg->header.message_type, old_msg_type,
- HVMSG_NONE) != old_msg_type)
+ if (!try_cmpxchg(&msg->header.message_type,
+ &old_msg_type, HVMSG_NONE))
return;
/*
diff --git a/drivers/hv/mshv_eventfd.c b/drivers/hv/mshv_eventfd.c
index 0b75ff1edb73..525e002758e4 100644
--- a/drivers/hv/mshv_eventfd.c
+++ b/drivers/hv/mshv_eventfd.c
@@ -128,8 +128,8 @@ static int mshv_vp_irq_try_set_vector(struct mshv_vp *vp,
u32 vector)
new_iv.vector[new_iv.vector_count++] = vector;
- if (cmpxchg(&vp->vp_register_page->interrupt_vectors.as_uint64,
- iv.as_uint64, new_iv.as_uint64) != iv.as_uint64)
+ if (!try_cmpxchg(&vp->vp_register_page->interrupt_vectors.as_uint64,
+ &iv.as_uint64, new_iv.as_uint64))
return -EAGAIN;
return 0;
--
2.53.0
