[Xen-devel] [PATCH] tools/libxl: make default of max event channels dependant on vcpus

[Juergen Gross <jgross@suse.com>]

Today the maximum number of event channels for a guest is defaulting
to 1023. For large guests with lots of vcpus this is not enough, as
e.g. the Linux kernel uses 7 event channels per vcpu, limiting the
guest to about 140 vcpus.

Instead of requiring to specify the allowed number of event channels
via the "event_channels" domain config option, make the default
depend on the maximum number of vcpus of the guest.

In order not to regress current configs use 1023 as the minimum
default setting.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 tools/libxl/libxl_create.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index e7cb2dbc2b..eddd0e98e5 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -226,7 +226,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
             b_info->iomem[i].gfn = b_info->iomem[i].start;
 
     if (!b_info->event_channels)
-        b_info->event_channels = 1023;
+        b_info->event_channels = min(1023, b_info->max_vcpus * 8 + 255);
 
     libxl__arch_domain_build_info_setdefault(gc, b_info);
     libxl_defbool_setdefault(&b_info->dm_restrict, false);
-- 
2.16.4