[Xen-changelog] [linux-2.6.18-xen] [IA64] improve response time in dom 0 at creating a guest domain

["Xen patchbot-linux-2.6.18-xen" <patchbot-linux-2.6.18-xen@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
# 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@xxxxxxxxxxxxxx>
---
 arch/ia64/xen/xcom_privcmd.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff -r 0deba952a6d3 -r 678ad99920c8 arch/ia64/xen/xcom_privcmd.c
--- a/arch/ia64/xen/xcom_privcmd.c      Mon Jul 28 17:24:40 2008 +0900
+++ b/arch/ia64/xen/xcom_privcmd.c      Tue Aug 05 12:19:38 2008 +0900
@@ -437,15 +437,18 @@ xencomm_privcmd_memory_reservation_op(pr
                 *   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;

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