2023-02-09 15:34:16

by Marcelo Tosatti

Subject: [PATCH v2 07/11] convert this_cpu_cmpxchg users to this_cpu_cmpxchg_local

this_cpu_cmpxchg was modified to atomic version, which
can be more costly than non-atomic version.

Switch users of this_cpu_cmpxchg to this_cpu_cmpxchg_local
(which preserves pre-non-atomic this_cpu_cmpxchg behaviour).

Signed-off-by: Marcelo Tosatti <[email protected]>

Index: linux-vmstat-remote/kernel/fork.c
===================================================================
--- linux-vmstat-remote.orig/kernel/fork.c
+++ linux-vmstat-remote/kernel/fork.c
@@ -203,7 +203,7 @@ static bool try_release_thread_stack_to_
unsigned int i;

for (i = 0; i < NR_CACHED_STACKS; i++) {
- if (this_cpu_cmpxchg(cached_stacks[i], NULL, vm) != NULL)
+ if (this_cpu_cmpxchg_local(cached_stacks[i], NULL, vm) != NULL)
continue;
return true;
}
Index: linux-vmstat-remote/kernel/scs.c
===================================================================
--- linux-vmstat-remote.orig/kernel/scs.c
+++ linux-vmstat-remote/kernel/scs.c
@@ -79,7 +79,7 @@ void scs_free(void *s)
*/

for (i = 0; i < NR_CACHED_SCS; i++)
- if (this_cpu_cmpxchg(scs_cache[i], 0, s) == NULL)
+ if (this_cpu_cmpxchg_local(scs_cache[i], 0, s) == NULL)
return;

kasan_unpoison_vmalloc(s, SCS_SIZE, KASAN_VMALLOC_PROT_NORMAL);

2023-03-02 20:55:54

by Peter Xu

Subject: Re: [PATCH v2 07/11] convert this_cpu_cmpxchg users to this_cpu_cmpxchg_local

On Thu, Feb 09, 2023 at 12:01:57PM -0300, Marcelo Tosatti wrote:
> this_cpu_cmpxchg was modified to atomic version, which
> can be more costly than non-atomic version.
>
> Switch users of this_cpu_cmpxchg to this_cpu_cmpxchg_local
> (which preserves pre-non-atomic this_cpu_cmpxchg behaviour).
>
> Signed-off-by: Marcelo Tosatti <[email protected]>

Yes afaict these are the only pieces that uses the helper besides vmstat
udpates.

Acked-by: Peter Xu <[email protected]>

--
Peter Xu