2021-07-13 07:27:43

by Zhen Lei

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

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 <[email protected]>
---
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

2021-08-20 22:14:42

by Bjorn Helgaas

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 <[email protected]>

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
>