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Re: [PATCH] rwlock: remove unneeded subtraction


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Tue, 15 Feb 2022 16:40:08 +0100
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  • Cc: Julien Grall <julien@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Tue, Feb 15, 2022 at 03:45:00PM +0100, Jan Beulich wrote:
> On 15.02.2022 15:16, Roger Pau Monné wrote:
> > I could add to the commit message:
> > 
> > "Originally _QR_BIAS was subtracted from the result of
> > atomic_add_return_acquire in order to prevent GCC from emitting an
> > unneeded ADD instruction. This being in the lock slow path such
> > optimizations don't seem likely to make any relevant performance
> > difference. Also modern GCC and CLANG versions will already avoid
> > emitting the ADD instruction."
> 
> ... I'm fine with this as explanation; I'd also be fine adding
> this to the description while committing.

Sure, thanks.

Roger.



 


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