[PATCH] xarray: inline xas_descend to improve performance

[PATCH] xarray: inline xas_descend to improve performance

[Long Li]

The commit 63b1898fffcd ("XArray: Disallow sibling entries of nodes")
modified the xas_descend function in such a way that it was no longer
being compiled as an inline function, because it increased the size of
xas_descend(), and the compiler no longer optimizes it as inline. This
had a negative impact on performance, xas_descend is called frequently
to traverse downwards in the xarray tree, making it a hot function.

Inlining xas_descend has been shown to significantly improve performance
by approximately 4.95% in the iozone write test.

  Machine: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz
  #iozone i 0 -i 1 -s 64g -r 16m -f /test/tmptest

Before this patch:

       kB    reclen    write   rewrite     read    reread
 67108864     16384  2230080   3637689 6 315197   5496027

After this patch:

       kB    reclen    write   rewrite     read    reread
 67108864     16384  2340360   3666175  6272401   5460782

Percentage change:
                       4.95%     0.78%   -0.68%    -0.64%

This patch introduces inlining to the xas_descend function. While this
change increases the size of lib/xarray.o, the performance gains in
critical workloads make this an acceptable trade-off.

Size comparison before and after patch:
.text		.data		.bss		file
0x3502		    0		   0		lib/xarray.o.before
0x3602		    0		   0		lib/xarray.o.after

Signed-off-by: Long Li <leo.lilong@huawei.com>
---
 lib/xarray.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index fbf1d1dd83bc..31e95b461c03 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -200,7 +200,7 @@ static void *xas_start(struct xa_state *xas)
 	return entry;
 }
 
-static void *xas_descend(struct xa_state *xas, struct xa_node *node)
+static inline void *xas_descend(struct xa_state *xas, struct xa_node *node)
 {
 	unsigned int offset = get_offset(xas->xa_index, node);
 	void *entry = xa_entry(xas->xa, node, offset);
-- 
2.31.1

Re: [PATCH] xarray: inline xas_descend to improve performance

[Andrew Morton]

On Mon, 15 Apr 2024 09:21:36 +0800 Long Li <leo.lilong@huawei.com> wrote:

> The commit 63b1898fffcd ("XArray: Disallow sibling entries of nodes")
> modified the xas_descend function in such a way that it was no longer
> being compiled as an inline function, because it increased the size of
> xas_descend(), and the compiler no longer optimizes it as inline. This
> had a negative impact on performance, xas_descend is called frequently
> to traverse downwards in the xarray tree, making it a hot function.
> 
> Inlining xas_descend has been shown to significantly improve performance
> by approximately 4.95% in the iozone write test.
> 
>   Machine: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz
>   #iozone i 0 -i 1 -s 64g -r 16m -f /test/tmptest
> 
> Before this patch:
> 
>        kB    reclen    write   rewrite     read    reread
>  67108864     16384  2230080   3637689 6 315197   5496027
> 
> After this patch:
> 
>        kB    reclen    write   rewrite     read    reread
>  67108864     16384  2340360   3666175  6272401   5460782
> 
> Percentage change:
>                        4.95%     0.78%   -0.68%    -0.64%
> 
> This patch introduces inlining to the xas_descend function. While this
> change increases the size of lib/xarray.o, the performance gains in
> critical workloads make this an acceptable trade-off.
> 
> Size comparison before and after patch:
> .text		.data		.bss		file
> 0x3502		    0		   0		lib/xarray.o.before
> 0x3602		    0		   0		lib/xarray.o.after
> 
> ...
>
> --- a/lib/xarray.c
> +++ b/lib/xarray.c
> @@ -200,7 +200,7 @@ static void *xas_start(struct xa_state *xas)
>  	return entry;
>  }
>  
> -static void *xas_descend(struct xa_state *xas, struct xa_node *node)
> +static inline void *xas_descend(struct xa_state *xas, struct xa_node *node)
>  {
>  	unsigned int offset = get_offset(xas->xa_index, node);
>  	void *entry = xa_entry(xas->xa, node, offset);

I thought gcc nowadays treats `inline' as avisory and still makes up
its own mind?

Perhaps we should use __always_inline here?

Re: [PATCH] xarray: inline xas_descend to improve performance

[Long Li]

On Mon, Apr 15, 2024 at 01:10:53PM -0700, Andrew Morton wrote:
> On Mon, 15 Apr 2024 09:21:36 +0800 Long Li <leo.lilong@huawei.com> wrote:
> 
> > The commit 63b1898fffcd ("XArray: Disallow sibling entries of nodes")
> > modified the xas_descend function in such a way that it was no longer
> > being compiled as an inline function, because it increased the size of
> > xas_descend(), and the compiler no longer optimizes it as inline. This
> > had a negative impact on performance, xas_descend is called frequently
> > to traverse downwards in the xarray tree, making it a hot function.
> > 
> > Inlining xas_descend has been shown to significantly improve performance
> > by approximately 4.95% in the iozone write test.
> > 
> >   Machine: Intel(R) Xeon(R) Gold 6240 CPU @ 2.60GHz
> >   #iozone i 0 -i 1 -s 64g -r 16m -f /test/tmptest
> > 
> > Before this patch:
> > 
> >        kB    reclen    write   rewrite     read    reread
> >  67108864     16384  2230080   3637689 6 315197   5496027
> > 
> > After this patch:
> > 
> >        kB    reclen    write   rewrite     read    reread
> >  67108864     16384  2340360   3666175  6272401   5460782
> > 
> > Percentage change:
> >                        4.95%     0.78%   -0.68%    -0.64%
> > 
> > This patch introduces inlining to the xas_descend function. While this
> > change increases the size of lib/xarray.o, the performance gains in
> > critical workloads make this an acceptable trade-off.
> > 
> > Size comparison before and after patch:
> > .text		.data		.bss		file
> > 0x3502		    0		   0		lib/xarray.o.before
> > 0x3602		    0		   0		lib/xarray.o.after
> > 
> > ...
> >
> > --- a/lib/xarray.c
> > +++ b/lib/xarray.c
> > @@ -200,7 +200,7 @@ static void *xas_start(struct xa_state *xas)
> >  	return entry;
> >  }
> >  
> > -static void *xas_descend(struct xa_state *xas, struct xa_node *node)
> > +static inline void *xas_descend(struct xa_state *xas, struct xa_node *node)
> >  {
> >  	unsigned int offset = get_offset(xas->xa_index, node);
> >  	void *entry = xa_entry(xas->xa, node, offset);
> 
> I thought gcc nowadays treats `inline' as avisory and still makes up
> its own mind?
> 
> Perhaps we should use __always_inline here?

Yes, I agree with you, I will send a new version. thanks!