xen: correctly check for pending events when restoring irq flags
authorDavid Vrabel <david.vrabel@citrix.com>
Thu, 26 Apr 2012 18:44:06 +0000 (19:44 +0100)
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Fri, 27 Apr 2012 20:04:21 +0000 (16:04 -0400)
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: stable@kernel.org
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
arch/x86/xen/xen-asm.S

index 79d7362..3e45aa0 100644 (file)
@@ -96,7 +96,7 @@ ENTRY(xen_restore_fl_direct)
 
        /* 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)