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