From: Uros Bizjak <ubizjak@gmail.com>
To: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org
Cc: Uros Bizjak <ubizjak@gmail.com>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
Long Li <longli@microsoft.com>
Subject: [PATCH] mshv: Use try_cmpxchg() instead of cmpxchg()
Date: Wed, 18 Feb 2026 11:25:37 +0100 [thread overview]
Message-ID: <20260218102604.178561-1-ubizjak@gmail.com> (raw)
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 <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>
---
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
next reply other threads:[~2026-02-18 10:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-18 10:25 Uros Bizjak [this message]
2026-02-18 11:00 ` [PATCH RESEND] mshv: Use try_cmpxchg() instead of cmpxchg() Uros Bizjak
2026-02-18 23:27 ` Wei Liu
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