[Xen-devel] [PATCH] xen: correctly check for pending events when restoring irq flags

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

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.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
I'd prefer to do more testing and benchmarking but the gains appear to
be significant.  e.g., lmbench3's 'lat_proc fork' test has improved
from 404 us to 357 us (~11% faster).
---
 arch/x86/xen/xen-asm.S |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S
index 79d7362..3e45aa0 100644
--- a/arch/x86/xen/xen-asm.S
+++ b/arch/x86/xen/xen-asm.S
@@ -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)
-- 
1.7.2.5


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