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

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

[Zhen Lei]

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@huawei.com>
---
 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

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

[Bjorn Helgaas]

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@huawei.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
>