xen/spinlock: Document the xen_nopvspin parameter.

Which disables in the ticketlock slowpath the Xen PV optimization's.
Useful for diagnosing issues and comparing benchmarks in
over-commit CPU scenarios.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7f9d4f53882c457ab8aa7f3e48c5fbbae7e903c2..b9589127b3ee803d8be90124855661415fc0f45a 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3412,6 +3412,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                                the unplug protocol
                        never -- do not unplug even if version check succeeds
 
+       xen_nopvspin    [X86,XEN]
+                       Disables the ticketlock slowpath using Xen PV
+                       optimizations.
+
        xirc2ps_cs=     [NET,PCMCIA]
                        Format:
                        <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]