This is a note to let you know that I've just added the patch titled
xen: correctly check for pending events when restoring irq flags
to the 3.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
xen-correctly-check-for-pending-events-when-restoring-irq-flags.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 7eb7ce4d2e8991aff4ecb71a81949a907ca755ac Mon Sep 17 00:00:00 2001
From: David Vrabel <[email protected]>
Date: Thu, 26 Apr 2012 19:44:06 +0100
Subject: xen: correctly check for pending events when restoring irq flags
From: David Vrabel <[email protected]>
commit 7eb7ce4d2e8991aff4ecb71a81949a907ca755ac upstream.
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)
Acked-by: Ian Campbell <[email protected]>
Signed-off-by: David Vrabel <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
arch/x86/xen/xen-asm.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- 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)
Patches currently in stable-queue which might be from [email protected]
are
queue-3.0/xen-correctly-check-for-pending-events-when-restoring-irq-flags.patch
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