Re: [PATCH] signal: avoid clearing TIF_SIGPENDING in recalc_sigpending() if unset

[Andrew Morton]

On Mon,  3 Mar 2025 14:49:08 +0100 Mateusz Guzik <mjguzik@xxxxxxxxx> wrote:

> Clearing is an atomic op and the flag is not set most of the time.
> 
> When creating and destroying threads in the same process with the
> pthread family, the primary bottleneck is calls to sigprocmask which
> take the process-wide sighand lock.
> 
> Avoiding the atomic gives me a 2% bump in start/teardown rate at 24-core
> scale.
> 

Neat.  Perhaps add an unlikely() also?

--- a/kernel/signal.c~signal-avoid-clearing-tif_sigpending-in-recalc_sigpending-if-unset-fix
+++ a/kernel/signal.c
@@ -177,7 +177,7 @@ static bool recalc_sigpending_tsk(struct
 void recalc_sigpending(void)
 {
 	if (!recalc_sigpending_tsk(current) && !freezing(current)) {
-		if (test_thread_flag(TIF_SIGPENDING))
+		if (unlikely(test_thread_flag(TIF_SIGPENDING)))
 			clear_thread_flag(TIF_SIGPENDING);
 	}
 }
_