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xen: correctly check for pending events when restoring irq flags

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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>
This commit is contained in:
David Vrabel 2012-04-26 19:44:06 +01:00 committed by Konrad Rzeszutek Wilk
parent b930fe5e1f
commit 7eb7ce4d2e
1 changed files with 1 additions and 1 deletions
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2
arch/x86/xen/xen-asm.S
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@ -96,7 +96,7 @@ ENTRY(xen_restore_fl_direct)
/* check for unmasked and pending */ /* check for unmasked and pending */
cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info) + XEN_vcpu_info_pending cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info) + XEN_vcpu_info_pending
jz 1f jnz 1f
2: call check_events 2: call check_events
1: 1:
ENDPATCH(xen_restore_fl_direct) ENDPATCH(xen_restore_fl_direct)