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Threads performance - allow signal handler to not call handler

PATCH In review Corey Minyard 2 participants 2 messages Mar 27, 2002

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Corey Minyard

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#0 lore raw

PATCH 1/1 Threads performance - allow signal handler to not call handler

This patch modfies i386 to add a flag to sa_flags in sigaction that will cause the signal handler to not be called (but all other side effects to occur). This may seem unusual, but signals are often used between threads to wake each other up, the signal handler is just a dummy and is pure overhead. With this patch, if the flag is set, the signal handler won't get called (thus saving the overhead of going in and out of userland for the handler), but it will still wake up sigsuspend() and select(). The beauty of this is the flag will be ignored on kernels without it, so it will still work, with just lower performance.

-Corey

arch/i386/kernel/signal.c renamed from arch/i386/kernel/signal.c.nocallhndlr +15 -12
@@ -558,21 +558,24 @@
 		}
 	}
 
-	/* Set up the stack frame */
-	if (ka->sa.sa_flags & SA_SIGINFO)
-		setup_rt_frame(sig, ka, info, oldset, regs);
-	else
-		setup_frame(sig, ka, oldset, regs);
-
 	if (ka->sa.sa_flags & SA_ONESHOT)
 		ka->sa.sa_handler = SIG_DFL;
 
-	if (!(ka->sa.sa_flags & SA_NODEFER)) {
-		spin_lock_irq(&current->sigmask_lock);
-		sigorsets(&current->blocked,&current->blocked,&ka->sa.sa_mask);
-		sigaddset(&current->blocked,sig);
-		recalc_sigpending(current);
-		spin_unlock_irq(&current->sigmask_lock);
+	/* Set up the stack frame */
+	if (! (ka->sa.sa_flags & SA_NOCALLHNDLR)) {
+		if (ka->sa.sa_flags & SA_SIGINFO)
+			setup_rt_frame(sig, ka, info, oldset, regs);
+		else
+			setup_frame(sig, ka, oldset, regs);
+
+		if (!(ka->sa.sa_flags & SA_NODEFER)) {
+			spin_lock_irq(&current->sigmask_lock);
+			sigorsets(&current->blocked,&current->blocked,
+				  &ka->sa.sa_mask);
+			sigaddset(&current->blocked,sig);
+			recalc_sigpending(current);
+			spin_unlock_irq(&current->sigmask_lock);
+		}
 	}
 }
include/asm-i386/signal.h renamed from include/asm-i386/signal.h.nocallhndlr +1 -0
@@ -91,6 +91,7 @@
 #define SA_RESTART	0x10000000
 #define SA_NODEFER	0x40000000
 #define SA_RESETHAND	0x80000000
+#define SA_NOCALLHNDLR	0x00800000 /* Don't really call the handler. */
 
 #define SA_NOMASK	SA_NODEFER
 #define SA_ONESHOT	SA_RESETHAND
#1 lore raw
Quoted 3 lines · [email protected] said:

With this patch, if the flag is set, the signal handler won't get called (thus saving the overhead of going in and out of userland for the handler), but it will still wake up sigsuspend() and select().

I've wanted this for UML as well. I have some empty signal handlers which exist for no reason other than to wake up pause/sigsuspend/et al.

Jeff