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 6315197 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 <[email protected]>
---
v2:
- Using '__always_inline' instead of 'inline' guarantees that xas_descend
will definitely be inlined.
lib/xarray.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/lib/xarray.c b/lib/xarray.c
index fbf1d1dd83bc..84faa433cd24 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -200,7 +200,8 @@ static void *xas_start(struct xa_state *xas)
return entry;
}
-static void *xas_descend(struct xa_state *xas, struct xa_node *node)
+static __always_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