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    Subject[ 11/75] xen: correctly check for pending events when restoring irq flags
    3.3-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    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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