On Thu, Dec 13, 2018 at 05:38:02PM +0100, Maxime Coquelin wrote:
On 12/13/18 1:34 PM, Jens Freimann wrote:
This is a basic implementation of packed virtqueues as specified in the
Virtio 1.1 draft. A compiled version of the current draft is available
at https://github.com/oasis-tcs/virtio-docs.git (or as .pdf at
https://github.com/oasis-tcs/virtio-docs/blob/master/virtio-v1.1-packed-wd10.pdf
A packed virtqueue is different from a split virtqueue in that it
consists of only a single descriptor ring that replaces available and
used ring, index and descriptor pointers.
Each descriptor is readable and writable and has a flags field. These flags
will mark if a descriptor is available or used. To detect new available
descriptors
even after the ring has wrapped, device and driver each have a
single-bit wrap counter that is flipped from 0 to 1 and vice versa every time
the last descriptor in the ring is used/made available.
With this patch set I see performance equal or slightly better (+2-3%) in a PVP
scenario compared to split virtqueues (v18.11 in host)
regards,
Jens
v11->v12:
* add a patch to disable control vq when packed vq is enabled.
I have a patch to support this but it needs a bit more work
and I think it shouldn't stop this series from being applied
* rework mergeable receive buffer code to be more efficient, by
batching descriptor refill, similar to what Maxime proposed for
split virtqueues
* removed unnecessary checks in virtio_recv_mergeable_pkts_packed
(Maxime)
* Did not merge receive functions as Maxime suggested because it seemed
to cause a small performance regression
* Move event_flags_shadow from patch 3 to 1 (Maxime)
* Did not merge xmit functions and call _split/_packed functions from
there because it seemed to cause small performance drop (-0.5%)
(Maxime)
v10-v11:
* this version includes some fixes from Tiwei, so I added his
Signed-off-by to some of the patches
* fix hang with mergable rx buffers (Tiwei)
* clean-up code and simplify buffer handling (Tiwei)
* rebase to current virtio-next master branch
v9-v10:
* don't mix index into buffer list and descriptors
* whitespace and formatting issues
* remove "VQ:" in dump virtqueue patch
* add extra packed vring struct to virtqueue and change function
prototypes and code accordingly
* move wrap_counters to virtqueue
* make if-conditions for packed and !packed more clear in
set_rxtx_funcs()
* initialize wrap counters in first patch, instead of rx and tx
implementation patch
* make virtio-user not supported with packed virtqueues, to
be fixed in other patch set?
v8-v9:
* fix virtio_ring_free_chain_packed() to handle descriptors
correctly in case of out-of-order
* fix check in virtqueue_xmit_cleanup_packed() to improve performance
v7->v8:
* move desc_is_used change to correct patch
* remove trailing newline
* correct xmit code, flags update and memory barrier
* move packed desc init to dedicated function, split
and packed variant
Jens Freimann (9):
net/virtio: vring init for packed queues
net/virtio: add packed virtqueue defines
net/virtio: add packed virtqueue helpers
net/virtio: dump packed virtqueue data
net/virtio: implement transmit path for packed queues
Note that the series build is broken until this patch.
I usually run 'git rebase -x "make"' to avoid. Must have missed it
this time, but will fix it.
regards,
Jens
