xen: correctly check for pending events when restoring irq flags

In xen_restore_fl_direct(), xen_force_evtchn_callback() was being
called even if no events were pending. This resulted in (depending on
workload) about a 100 times as many xen_version hypercalls as
necessary.

Fix this by correcting the sense of the conditional jump.

This seems to give a significant performance benefit for some
workloads.

There is some subtle tricksy "..since the check here is trying to
check both pending and masked in a single cmpw, but I think this is
correct. It will call check_events now only when the combined
mask+pending word is 0x0001 (aka unmasked, pending)." (Ian)

CC: [e-mail]
Acked-by: Ian Campbell <[e-mail]>
Signed-off-by: David Vrabel <[e-mail]>
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>

arch/x86/xen/xen-asm.S

···
 
 	/* check for unmasked and pending */
 	cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info) + XEN_vcpu_info_pending
-	jz 1f
+	jnz 1f
 2:	call check_events
 1:
 ENDPATCH(xen_restore_fl_direct)