[Xen-devel] [PATCHv1 6/6] evtchn: pad struct evtchn to 64 bytes

[David Vrabel <david.vrabel@xxxxxxxxxx>]

The number of struct evtchn in a page must be a power of two.  Under
some workloads performance is improved slightly by padding struct
evtchn to 64 bytes (a cache line), thus putting the per-channel locks
into their own cache line.

This does not decrease the number of struct evtchn's per-page.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
---
I'm not sure we actually want to do this.  I think it would be better
to pack the struct evtchn and use vmap to turn the pages into a linear
array for quicker lookup.
---
 xen/include/xen/sched.h |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 292e28f..0749c43 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -110,8 +110,8 @@ struct evtchn
     u8 priority;
     u8 last_priority;
     u16 last_vcpu_id;
-#ifdef XSM_ENABLE
     union {
+#ifdef XSM_ENABLE
 #ifdef XSM_NEED_GENERIC_EVTCHN_SSID
         /*
          * If an XSM module needs more space for its event channel context,
@@ -127,8 +127,9 @@ struct evtchn
          */
         u32 flask_sid;
 #endif
-    } ssid;
 #endif
+        u8 __pad[24]; /* Round size to power of two. */
+    } ssid;
 };
 
 int  evtchn_init(struct domain *d); /* from domain_create */
-- 
1.7.10.4


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