From: Tetsu Yamamoto <tyamamot@redhat.com>
Date: Tue, 12 Aug 2008 16:07:27 -0400
Subject: [xen] ia64: speed up hypercall for guest domain creation
Message-id: 20080812200727.4832.75960.sendpatchset@pq0-1.lab.bos.redhat.com
O-Subject: [RHEL5.3 PATCH 5/7] xen-ia64: improve response time in dom 0 at creating a guest domain
Bugzilla: 456171
RH-Acked-by: Chris Lalancette <clalance@redhat.com>
RH-Acked-by: Bill Burns <bburns@redhat.com>

bz456171
# HG changeset patch
# User Isaku Yamahata <yamahata@valinux.co.jp>
# Date 1217906378 -32400
# Node ID 678ad99920c897f247c37d3de14827c547e664c5
# Parent  0deba952a6d3d2a58c404feefea2bccb3071089a
[IA64] improve response time in dom 0 at creating a guest domain

The hypercall takes several hundred mili seconds,
and it takes around 5 mili seconds with my new patch.
Time of one hypercall should be smaller than a vcpu time slice.

Signed-off-by: Akio Takebe <takebe_akio@jp.fujitsu.com>

diff --git a/arch/ia64/xen/xcom_privcmd.c b/arch/ia64/xen/xcom_privcmd.c
index ec2e70d..a5b6b12 100644
--- a/arch/ia64/xen/xcom_privcmd.c
+++ b/arch/ia64/xen/xcom_privcmd.c
@@ -83,15 +83,18 @@ xencomm_privcmd_memory_reservation_op(privcmd_hypercall_t *hypercall)
 		 *   may cause the soft lockup warning.
 		 *   In order to avoid the warning, we limit
 		 *   the number of extents and repeat the hypercall.
-		 *   The following value is determined by experimentation.
-		 *   If the following limit causes soft lockup warning,
+		 *   The following value is determined by evaluation.
+		 *   Time of one hypercall should be smaller than
+		 *   a vcpu time slice. The time with current
+		 *   MEMORYOP_MAX_EXTENTS is around 5 msec.
+		 *   If the following limit causes some issues,
 		 *   we should decrease this value.
 		 *
 		 *   Another way would be that start with small value and
 		 *   increase adoptively measuring hypercall time.
 		 *   It might be over-kill.
 		 */
-#define MEMORYOP_MAX_EXTENTS	(MEMORYOP_XENCOMM_LIMIT / 4)
+#define MEMORYOP_MAX_EXTENTS	(MEMORYOP_XENCOMM_LIMIT / 512)
 
 		while (nr_extents > 0) {
 			xen_ulong_t nr_tmp = nr_extents;