Re: [tip:timers/core] [posix] 1535cb8028: stress-ng.epoll.ops_per_sec 36.2% regression

[Eric Dumazet]

On Thu, Mar 27, 2025 at 9:26 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:

> We could place all these atomic fields in separate cache lines,
> to keep read-only fields shared as much as possible.
>

Following one-liner seems good enough to separate the 4 atomics used
to control/limit

UCOUNT_RLIMIT_NPROC, UCOUNT_RLIMIT_MSGQUEUE, UCOUNT_RLIMIT_SIGPENDING,
UCOUNT_RLIMIT_MEMLOCK,


diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index 7183e5aca282..6cc3fbec3632 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -120,7 +120,7 @@ struct ucounts {
        kuid_t uid;
        atomic_t count;
        atomic_long_t ucount[UCOUNT_COUNTS];
-       atomic_long_t rlimit[UCOUNT_RLIMIT_COUNTS];
+       atomic_long_t ____cacheline_aligned_in_smp rlimit[UCOUNT_RLIMIT_COUNTS];
 };

 extern struct user_namespace init_user_ns;