INSTALL.DPDK.md: Update ivshmem page size restrictions

Update ivshmem restrictions to indicate that ivshmem does
not currently support small pages when sharing with a guest
operating system.

Reported-by: Daniele Di Proietto <diproiettod@vmware.com>
Signed-off-by: Mark D. Gray <mark.d.gray@intel.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/INSTALL.DPDK.md b/INSTALL.DPDK.md
index a5b3494..aae97a5 100644 (file)
--- a/INSTALL.DPDK.md
+++ b/INSTALL.DPDK.md
@@ -555,10 +555,16 @@ Restrictions:
   - DPDK-vHost support works with 1G huge pages.
 
   ivshmem:
-  - The shared memory is currently restricted to the use of a 1GB
-    huge pages.
-  - All huge pages are shared amongst the host, clients, virtual
-    machines etc.
+  - If you run Open vSwitch with smaller page sizes (e.g. 2MB), you may be
+    unable to share any rings or mempools with a virtual machine.
+    This is because the current implementation of ivshmem works by sharing
+    a single 1GB huge page from the host operating system to any guest
+    operating system through the Qemu ivshmem device. When using smaller
+    page sizes, multiple pages may be required to hold the ring descriptors
+    and buffer pools. The Qemu ivshmem device does not allow you to share
+    multiple file descriptors to the guest operating system. However, if you
+    want to share dpdkr rings with other processes on the host, you can do
+    this with smaller page sizes.
 
 Bug Reporting:
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