Commit 05976960 authored by Uros Bizjak's avatar Uros Bizjak Committed by Wei Liu
Browse files

mshv: Use try_cmpxchg() instead of cmpxchg() 



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: default avatarUros Bizjak <ubizjak@gmail.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Long Li <longli@microsoft.com>
Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
parent 705d01c8

drivers/hv/hyperv_vmbus.h

+2 −2
Original line number Diff line number Diff line
@@ -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;



	/*

drivers/hv/mshv_eventfd.c

+2 −2
Original line number Diff line number Diff line
@@ -129,8 +129,8 @@ 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;