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

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Message-ID: <1692874334-39255-1-git-send-email-huangshaobo3@xiaomi.com>
Date:   Thu, 24 Aug 2023 03:52:14 -0700
From:   sparkhuang <huangshaobo3@...omi.com>
To:     <tglx@...utronix.de>
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, 24 Aug 2023 11:04:16 +0200, Thomas Gleixner wrote:
> 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?

There is nothing wrong with the current code,
using desc.pci.msi_attrib.is_64 does not solve any problems,
thank you very much for reviewing comments.

Thanks,
sparkhuang
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