It's not necessary to populate guest memory from vhost side unless
zerocopy is enabled or users want better performance.
Update the doc for guest memory requirement clarification.
Cc: maxime.coque...@redhat.com
Signed-off-by: Jianfeng Tan <jianfeng....@intel.com>
---
doc/guides/prog_guide/vhost_lib.rst | 21 +++++++++++++++++++++
doc/guides/sample_app_ug/vhost.rst | 9 ---------
lib/librte_vhost/vhost_user.c | 4 +++-
3 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/doc/guides/prog_guide/vhost_lib.rst
b/doc/guides/prog_guide/vhost_lib.rst
index 18227b6..f474736 100644
--- a/doc/guides/prog_guide/vhost_lib.rst
+++ b/doc/guides/prog_guide/vhost_lib.rst
@@ -214,6 +214,27 @@ the vhost device from the data plane.
When the socket connection is closed, vhost will destroy the device.
+Guest memory requirement
+------------------------
+
+* Memory pre-allocation
+
+ For non-zerocopy, guest memory pre-allocation is not a must. This can help
+ save of memory. If users really want the guest memory to be pre-allocated
+ (e.g., for performance reason), we can add option ``-mem-prealloc`` when
+ starting QEMU. Or, we can lock all memory at vhost side which will force
+ memory to be allocated when mmap at vhost side; option --mlockall in
+ ovs-dpdk is an example in hand.
+
+ For zerocopy, we force the VM memory to be pre-allocated at vhost lib when
+ mapping the guest memory; and also we need to lock the memory to prevent
+ pages being swapped out to disk.
+
+* Memory sharing
+
+ Make sure ``share=on`` QEMU option is given. vhost-user will not work with
+ a QEMU version without shared memory mapping.
+
Vhost supported vSwitch reference
---------------------------------
diff --git a/doc/guides/sample_app_ug/vhost.rst
b/doc/guides/sample_app_ug/vhost.rst
index a4bdc6a..da161a9 100644
--- a/doc/guides/sample_app_ug/vhost.rst
+++ b/doc/guides/sample_app_ug/vhost.rst
@@ -175,15 +175,6 @@ Common Issues
The command above indicates how many hugepages are free to support QEMU's
allocation request.
-* vhost-user will not work with QEMU without the ``-mem-prealloc`` option
-
- The current implementation works properly only when the guest memory is
- pre-allocated.
-
-* vhost-user will not work with a QEMU version without shared memory mapping:
-
- Make sure ``share=on`` QEMU option is given.
-
* Failed to build DPDK in VM
Make sure "-cpu host" QEMU option is given.
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 90ed211..9bd0391 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -644,6 +644,7 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct
VhostUserMsg *pmsg)
uint64_t mmap_offset;
uint64_t alignment;
uint32_t i;
+ int populate;
int fd;
if (dev->mem && !vhost_memory_changed(&memory, dev->mem)) {
@@ -714,8 +715,9 @@ vhost_user_set_mem_table(struct virtio_net *dev, struct
VhostUserMsg *pmsg)
}
mmap_size = RTE_ALIGN_CEIL(mmap_size, alignment);
+ populate = (dev->dequeue_zero_copy) ? MAP_POPULATE : 0;
mmap_addr = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
- MAP_SHARED | MAP_POPULATE, fd, 0);
+ MAP_SHARED | populate, fd, 0);
if (mmap_addr == MAP_FAILED) {
RTE_LOG(ERR, VHOST_CONFIG,
--
2.7.4
