From: "Jan Beulich" <jbeulich@novell.com>
Subject: Re: [Patch 2 of 2]: PV-domain SMP performance Linux-part
Date: Wed, 17 Dec 2008 15:06:31 +0000
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>--- a/include/asm-x86_64/mach-xen/asm/irqflags.h	Sat Dec 13 =
16:00:43 2008 +0000
>+++ b/include/asm-x86_64/mach-xen/asm/irqflags.h	Wed Dec 17 =
13:12:53 2008 +0100
>@@ -33,8 +33,12 @@ do {							=
		\
> 	vcpu_info_t *_vcpu;						\
> 	barrier();							\
> 	_vcpu =3D current_vcpu_info();		\
>-	if ((_vcpu->evtchn_upcall_mask =3D (x)) =3D=3D 0) {			=
\
>+	if ( !(x) ) {							\

This isn't correct, as it breaks 0->1 transitions (there are a few =
instances of
this in the kernel).

>+		_vcpu->no_desched =3D 0;					=
\
>+	        _vcpu->evtchn_upcall_mask =3D 0;				=
\
> 		barrier(); /* unmask then check (avoid races) */	\
>+		if ( unlikely(_vcpu->desched_delay) )			\
>+			(void)((HYPERVISOR_sched_op(SCHEDOP_yield, =
_vcpu))?:0); \

Why not just cast the function result to void? Likewise further below...

> 		if ( unlikely(_vcpu->evtchn_upcall_pending) )		\
> 			force_evtchn_callback();			\
> 	}								\

Jan