[ovs-dev] [PATCH v6 0/6] OVS-DPDK rxq to pmd assignment improvements.

[Kevin Traynor]

For the DPDK datapath, by default rxqs are assigned to available pmds
in round robin order with no weight or priority.

It can happen that some very busy queues are handled by one pmd which
does not have enough cycles to prevent packets being dropped on them.
While at the same time another pmd which handles queues with no traffic
on them is essentially idle.

Rxq to pmd assignment happens as a result of a number of events and
when it does, the same unweighted round robin approach is applied
each time.

This patchset proposes to improve the round robin nature of rxq to pmd
assignment by counting the processing cycles used by the rxqs during
their operation and incorporating that data into assignment.

Before assigning in a round robin manner, the rxqs will be sorted in
order of the processing cycles they have been consuming. Assuming
multiple pmds, this ensures that the rxqs measured to be using the
most processing cycles will be assigned to different cores.

In some cases the measured cycles for an rxq may be not available as
the rxq is new or may not be useful for assignment as traffic patterns
may change.  In those cases the code will essentially fallback to being
round round similar to what currently exists. However, in the case
where data is available and a reliable indication of future rxq cycles
consumption, rxq to pmd distribution will be much improved.

V5 -> V6
========
Minor changes to 2/6, 3/6, 4/6, 5/6 from Darrell's review comments.

V4 -> V5
========
Changed history of rxq considered during assignment to 1 min. In order
to have data available quicker than 1 min and not to be using up to
1 min old data, introduced storing of data in multiple intervals
similar to suggestion by Darrell. Some minor name changes to reflect
this.

2/6 Added storage for multiple intervals
3/6 Store cycles into interval
4/6 Sum cycles from intervals and use total for assignment

V3 -> V4
========
4/6
Rebased to accomodate new cross numa assigment.

V2 -> V3
========
Dropped v2 1/7 as not reusing dpcls optimisation interval anymore

2/6
Moved unused functions to 3/6 to avoid compiler warning

3/6
Made pmd rxq interval independent from dpcls opt interval

4/6
Moved docs about rebalance command to when it is available in 6/6
Added logging info for pmd to rxq assignment

5/6
Added an example to docs

6/6
Noted in commit msg that Jan requested this for testing purposes

V1 -> V2
========
Dropped Ciara's patch to change how pmd cycles are counted as it merged.

6/7: Rebased unit tests.


Kevin Traynor (6):
  dpif-netdev: Change polled_queue to use dp_netdev_rxq.
  dpif-netdev: Add rxq processing cycle counters.
  dpif-netdev: Count the rxq processing cycles for an rxq.
  dpif-netdev: Change rxq_scheduling to use rxq processing cycles.
  dpif-netdev: Change pmd selection order.
  dpif-netdev: Add ovs-appctl dpif-netdev/pmd-rxq-rebalance.

 Documentation/howto/dpdk.rst |  26 ++++
 lib/dpif-netdev.c            | 298 ++++++++++++++++++++++++++++++++++++-------
 tests/pmd.at                 |   2 +-
 vswitchd/ovs-vswitchd.8.in   |   2 +
 4 files changed, 284 insertions(+), 44 deletions(-)

-- 
1.8.3.1