On Mon, Nov 20, 2023 at 03:11:31PM +0800, kernel test robot wrote:
>
>
> Hello,
>
> kernel test robot noticed a -2.9% regression of will-it-scale.per_thread_ops on:
>
>
> commit: 0ede61d8589cc2d93aa78230d74ac58b5b8d0244 ("file: convert to SLAB_TYPESAFE_BY_RCU")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
> 93faf426e3cc000c 0ede61d8589cc2d93aa78230d74
> ---------------- ---------------------------
> %stddev %change %stddev
> \ | \
[snip]
> 30.90 ± 4% -20.6 10.35 ± 2% perf-profile.self.cycles-pp.__fget_light
> 0.00 +26.5 26.48 perf-profile.self.cycles-pp.__get_file_rcu
[snip]
So __fget_light now got a func call.
I don't know if this is worth patching (and benchmarking after), but I
if sorting this out is of interest, triviality below is probably the
easiest way out:
diff --git a/fs/file.c b/fs/file.c
index 5fb0b146e79e..d8d3e18800c4 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -856,14 +856,14 @@ void do_close_on_exec(struct files_struct *files)
spin_unlock(&files->file_lock);
}
-static struct file *__get_file_rcu(struct file __rcu **f)
+static __always_inline struct file *__get_file_rcu(struct file __rcu **f)
{
struct file __rcu *file;
struct file __rcu *file_reloaded;
struct file __rcu *file_reloaded_cmp;
file = rcu_dereference_raw(*f);
- if (!file)
+ if (unlikely(!file))
return NULL;
if (unlikely(!atomic_long_inc_not_zero(&file->f_count)))
@@ -891,7 +891,7 @@ static struct file *__get_file_rcu(struct file __rcu **f)
* If the pointers don't match the file has been reallocated by
* SLAB_TYPESAFE_BY_RCU.
*/
- if (file == file_reloaded_cmp)
+ if (likely(file == file_reloaded_cmp))
return file_reloaded;
fput(file);
