[dpdk-dev] [RFC PATCH 0/3] *** SUBJECT HERE ***

Konstantin Ananyev konstantin.ananyev at intel.com
Fri Dec 1 15:47:59 CET 2017

The series introduces 2 main changes:

1.Introduce a separate data structure (rte_eth_queue_local)
to store local to given process (i.e. no-shareable) information
for each configured rx/tx queue.
Memory for that structure is allocated/freed dynamically during
Reserve a space for queue specific (rx|tx)_pkt_burst(),
tx_pkt_prepare() function pointers inside that structure.
Move rx/tx callback related information inside that structure.
That introduces a change in current behavior: all callbacks for
un-configured queues will be automatically removed.
Also as size of struct rte_eth_dev changes that patch is an ABI breakage,
so deprecation notice for 18.05 is filled.
Further suggestions how to introduce the same functionality
without ABI breakage are welcome.

2. Make it safe to remove rx/tx callback at runtime.
Right now it is not possible for the application to figure out
when it is safe to free removed callback handle and
associated with it resources(unless the queue is stopped).
That's probably not a big problem if all callbacks are static
hange through whole application lifetime)
and/or application doesn't allocate any resources for the callback handler.
Though if callbacks have to be added/removed dynamically and
callback handler would require more resources to operate properly -
then it might become an issue.
So patch #2 fixes that problem - now as soon as
rte_eth_remove_(rx|tx)_callback() completes successfully, application
can safely free all associated with the removed callback resources.

Performance impact:
If application doesn't use RX/TX callbacks, then the tests I run didn't
reveal any performance degradation.
Though if application do use RX/TX callbacks - patch #2 does introduce
some slowdown.
To be more specific here, on BDW (E5-2699 v4) 2.2GHz, 4x10Gb (X520-4)
with http://dpdk.org/dev/patchwork/patch/31864/ patch installed I got:
1) testpmd ... --latencystats=1 - slowdown < 1%
2) examples//l3fwd ... --parse-ptype - - slowdown < 1%
3) examples/rxtx_callbacks - slowdown ~8%
All that in terms of packet throughput (Mpps).

Ability to safely remove callbacks at runtime implies
some sort of synchronization.
Even I tried to make it as light as possible,
probably some slowdown is unavoidable.
Of course instead of introducing these changes at rte_ethdev layer
similar technique could be applied on individual callback basis.
In that case it would be up to callback writer/installer to decide
does he/she need a removable at runtime callback or not.
Though in that case, each installed callback might introduce extra
synchronization overhead and slowdown.

Konstantin Ananyev (3):
  ethdev: introduce eth_queue_local
  ethdev: make it safe to remove rx/tx callback at runtime
  doc: ethdev ABI change deprecation notice

 doc/guides/rel_notes/deprecation.rst |   5 +
 lib/librte_ether/rte_ethdev.c        | 390 ++++++++++++++++++++++-------------
 lib/librte_ether/rte_ethdev.h        | 174 ++++++++++++----
 3 files changed, 387 insertions(+), 182 deletions(-)


More information about the dev mailing list