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

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Message-ID: <1692862032-37839-1-git-send-email-huangshaobo3@xiaomi.com>
Date:   Thu, 24 Aug 2023 00:27:12 -0700
From:   <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 Wed, 23 Aug 2023 16:15:27 +0200, Thomas Gleixner wrote:
> On Fri, Aug 18 2023 at 07:26, 黄少波 wrote:

> Your patch is corrupt:

>  Applying: Subject: [PATCH] pci/msi: remove redundant calculation in msi_setup_msi_desc
>  error: corrupt patch at line 12

> It's DOS mangled and whitespace damaged.

Very sorry, may have accidentally broken the patch format,
and will make sure to use plain text next time.

> > Whether to support 64-bit address status has been calculated before,
> > and the calculation result can be used directly afterwards, so use
> > msi_attrib.is_64 to avoid double calculation.

> 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?

> Thanks,

>         tglx

thanks,
sparkhuang
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