Changes in v2:
- Remove the configure macro
- Enable simple R/TX processing when user specifies simple txq flags
- Reword some comments and commit messages
Changes in v3:
- Remove unnecessary NULL test for rte_free
- Remove unnecessary assign of local var after free
- Remove return at the end of void function
- Remove always_inline attribute for virtio_xmit_cleanup
- Reword some commit messages
- Add TODO in the commit message of simple tx patch
In DPDK based switching enviroment, mostly vhost runs on a dedicated core
while virtio processing in guest VMs runs on other different cores.
Take RX for example, with generic implementation, for each guest buffer,
a) virtio driver allocates a descriptor from free descriptor list
b) modify the entry of avail ring to point to allocated descriptor
c) after packet is received, free the descriptor
When vhost fetches the avail ring, it need to fetch the modified L1 cache from
virtio core, which is a heavy cost in current CPU implementation.
This idea of this optimization is:
allocate the fixed descriptor for each entry of avail ring, so avail ring
will
always be the same during the run.
This removes L1M cache transfer from virtio core to vhost core for avail ring.
(Note we couldn't avoid the cache transfer for descriptors).
Besides, descriptor allocation and free operation is eliminated.
This also makes vector procesing possible to further accelerate the processing.
This is the layout for the avail ring(take 256 ring entries for example), with
each entry pointing to the descriptor with the same index.
avail
idx
+
|
+----+----+---+-------------+------+
| 0 | 1 | 2 | ... | 254 | 255 | avail ring
+-+--+-+--+-+-+---------+---+--+---+
| | | | | |
| | | | | |
v v v | v v
+-+--+-+--+-+-+---------+---+--+---+
| 0 | 1 | 2 | ... | 254 | 255 | desc ring
+----+----+---+-------------+------+
|
|
+----+----+---+-------------+------+
| 0 | 1 | 2 | | 254 | 255 | used ring
+----+----+---+-------------+------+
|
+
This is the ring layout for TX.
As we need one virtio header for each xmit packet, we have 128 slots available.
++
||
||
+-----+-----+-----+--------------+------+------+------+
| 0 | 1 | ... | 127 || 128 | 129 | ... | 255 | avail ring
+--+--+--+--+-----+---+------+---+--+---+------+--+---+
| | | || | | |
v v v || v v v
+--+--+--+--+-----+---+------+---+--+---+------+--+---+
| 127 | 128 | ... | 255 || 127 | 128 | ... | 255 | desc ring for
virtio_net_hdr
+--+--+--+--+-----+---+------+---+--+---+------+--+---+
| | | || | | |
v v v || v v v
+--+--+--+--+-----+---+------+---+--+---+------+--+---+
| 0 | 1 | ... | 127 || 0 | 1 | ... | 127 | desc ring for tx dat
+-----+-----+-----+--------------+------+------+------+
||
||
++
Performance boost could be observed only if the virtio backend isn't the
bottleneck or in VM2VM
case.
There are also several vhost optimization patches to be submitted later.
Huawei Xie (7):
virtio: add virtio_rxtx.h header file
virtio: add software rx ring, fake_buf into virtqueue
virtio: rx/tx ring layout optimization
virtio: fill RX avail ring with blank mbufs
virtio: virtio vec rx
virtio: simple tx routine
virtio: choose simple rx/tx func
drivers/net/virtio/Makefile | 2 +-
drivers/net/virtio/virtio_ethdev.c | 12 +-
drivers/net/virtio/virtio_ethdev.h | 5 +
drivers/net/virtio/virtio_rxtx.c | 53 ++++-
drivers/net/virtio/virtio_rxtx.h | 39 ++++
drivers/net/virtio/virtio_rxtx_simple.c | 401 ++++++++++++++++++++++++++++++++
drivers/net/virtio/virtqueue.h | 5 +
7 files changed, 513 insertions(+), 4 deletions(-)
create mode 100644 drivers/net/virtio/virtio_rxtx.h
create mode 100644 drivers/net/virtio/virtio_rxtx_simple.c
--
1.8.1.4
