linux-kernel - Re: [PATCH 1/1] PCI: Optimize pci_resource_len() to reduce the binary size of kernel

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Date:   Fri, 20 Aug 2021 17:11:57 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PCI: Optimize pci_resource_len() to reduce the
 binary size of kernel

On Tue, Jul 13, 2021 at 03:22:36PM +0800, Zhen Lei wrote:
> pci_resource_end() can be 0 only when pci_resource_start() is 0.
> Otherwise, it is definitely an error. In this case, pci_resource_len()
> should be regarded as 0. Therefore, determining whether
> pci_resource_start() and pci_resource_end() are both 0 can be reduced to
> determining only whether pci_resource_end() is 0.
> 
> Although only one condition judgment is reduced, the macro function
> pci_resource_len() is widely referenced in the kernel. I used defconfig to
> compile the latest kernel on X86, and its binary code size was reduced by
> about 3KB.
> 
> Before:
>  [ 2] .rela.text        RELA             0000000000000000  093bfcb0
>       0000000001a67168  0000000000000018   I      68     1     8
> 
> After:
>  [ 2] .rela.text        RELA             0000000000000000  093bfcb0
>       0000000001a66598  0000000000000018   I      68     1     8
> 
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>

Applied to pci/resource for v5.15, thanks!

> ---
>  include/linux/pci.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 540b377ca8f6..23ef1a15eb5d 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1881,9 +1881,7 @@ int pci_iobar_pfn(struct pci_dev *pdev, int bar, struct vm_area_struct *vma);
>  #define pci_resource_end(dev, bar)	((dev)->resource[(bar)].end)
>  #define pci_resource_flags(dev, bar)	((dev)->resource[(bar)].flags)
>  #define pci_resource_len(dev,bar) \
> -	((pci_resource_start((dev), (bar)) == 0 &&	\
> -	  pci_resource_end((dev), (bar)) ==		\
> -	  pci_resource_start((dev), (bar))) ? 0 :	\
> +	((pci_resource_end((dev), (bar)) == 0) ? 0 :	\
>  							\
>  	 (pci_resource_end((dev), (bar)) -		\
>  	  pci_resource_start((dev), (bar)) + 1))
> -- 
> 2.25.1
>