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Date: Mon, 15 Apr 2024 13:31:56 -0300
From: Jason Gunthorpe <jgg@ziepe.ca>
To: Uros Bizjak <ubizjak@gmail.com>
Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org,
	David Woodhouse <dwmw2@infradead.org>,
	Lu Baolu <baolu.lu@linux.intel.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>, Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH] iommu/intel: Use try_cmpxchg64{,_local}() in iommu.c
Message-ID: <20240415163156.GQ223006@ziepe.ca>
References: <20240414162454.49584-1-ubizjak@gmail.com>
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In-Reply-To: <20240414162454.49584-1-ubizjak@gmail.com>

On Sun, Apr 14, 2024 at 06:23:11PM +0200, Uros Bizjak wrote:
> Replace this pattern in iommu.c:
> 
>     cmpxchg64{,_local}(*ptr, 0, new) != 0
> 
> ... with the simpler and faster:
> 
>     !try_cmpxchg64{,_local}(*ptr, &tmp, new)
> 
> The x86 CMPXCHG instruction returns success in the ZF flag, so this change
> saves a compare after the CMPXCHG.
> 
> No functional change intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Lu Baolu <baolu.lu@linux.intel.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Will Deacon <will@kernel.org>
> Cc: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/intel/iommu.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason