linux-kernel - Re: Subject: [PATCH] pci/msi: remove redundant calculation in msi_setup_msi

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Message-ID: <87o7iwdd67.ffs@tglx>
Date:   Thu, 24 Aug 2023 11:04:16 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     huangshaobo3@...omi.com
Cc:     bhelgaas@...gle.com, chenwei29@...omi.com, darwi@...utronix.de,
        huangshaobo3@...omi.com, jgg@...pe.ca, kevin.tian@...el.com,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        weipengliang@...omi.com, wengjinfei@...omi.com
Subject: Re: Subject: [PATCH] pci/msi: remove redundant calculation in
 msi_setup_msi_desc

On Thu, Aug 24 2023 at 00:27, huangshaobo3@...omi.com wrote:
> On Wed, 23 Aug 2023 16:15:27 +0200, Thomas Gleixner wrote:
>> I'm not seeing what this solves:
>
>> > -       if (control & PCI_MSI_FLAGS_64BIT)
>> > +       if (desc.pci.msi_attrib.is_64)
>
>> Both variants resolve to a test of a bit and a conditional instruction
>> on the result. It's exactly zero difference in terms of "calculation".
>
>> So all this does is change the memory location to test. Not more not
>> less. It does not generate better code and does not save anything.
>
> It may not be appropriate to write to eliminate duplicate calculations,
> can it be proposed again with clean code?

What's wrong with the existing code?