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Date: Wed, 18 Feb 2026 23:27:47 +0000
From: Wei Liu <wei.liu@kernel.org>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
	"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: Re: [PATCH RESEND] mshv: Use try_cmpxchg() instead of cmpxchg()
Message-ID: <20260218232747.GK2236050@liuwe-devbox-debian-v2.local>
References: <20260218102604.178561-1-ubizjak@gmail.com>
 <20260218110041.179949-1-ubizjak@gmail.com>
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In-Reply-To: <20260218110041.179949-1-ubizjak@gmail.com>

On Wed, Feb 18, 2026 at 12:00:18PM +0100, Uros Bizjak wrote:
> 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>

Applied. Thanks.