[dpdk-dev] [PATCH v12 00/10] implement packed virtqueues

Jens Freimann jfreimann at redhat.com
Thu Dec 13 23:36:42 CET 2018

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
>>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)
>>  * 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)
>>  * 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
>>  * 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?
>>  * 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
>>  * 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.


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