On Thu, 6 Apr 2023 22:47:21 +0200 Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> The sigqueue caching originated in the PREEMPT_RT tree. A few of the
> applications, that were ported to Linux, were ported from OS-9. Sending
> notifications from one task to another via a signal was a common
> communication model there and so the applications are heavy signal
> users. Removing the allocation reduces the critical path, avoids locks
> and so lowers the maximal latency of the task while sending a signal.
This is needed only if slab does not work for you.
Why not make it work better instead of peeling slab one more off just to
make signal/rt richer?
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -432,7 +432,18 @@ static struct sigqueue *
> return NULL;
> =20
> if (override_rlimit || likely(sigpending <=3D task_rlimit(t, RLIMIT_SIGPE=
> NDING))) {
> - q =3D kmem_cache_alloc(sigqueue_cachep, gfp_flags);
> +
> + if (!sigqueue_flags) {
> + struct sighand_struct *sighand =3D t->sighand;
> +
> + lockdep_assert_held(&sighand->siglock);
> + if (sighand->sigqueue_cache) {
> + q =3D sighand->sigqueue_cache;
> + sighand->sigqueue_cache =3D NULL;
> + }
> + }
> + if (!q)
> + q =3D kmem_cache_alloc(sigqueue_cachep, gfp_flags);
> } else {
> print_dropped_signal(sig);
> }
