Messages in this thread Patch in this message | | | Date | Fri, 04 May 2012 13:42:35 -0700 | From | Greg KH <> | Subject | [ 11/75] xen: correctly check for pending events when restoring irq flags |
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3.3-stable review patch. If anyone has any objections, please let me know.
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From: David Vrabel <david.vrabel@citrix.com>
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 <ian.campbell@citrix.com> Signed-off-by: David Vrabel <david.vrabel@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- 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)
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