Re: [PATCH v3] event/dsw: support explicit release only mode

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2024-06-08 08:14, Jerin Jacob wrote:
> On Fri, Jun 7, 2024 at 7:17 PM Mattias Rönnblom
> <mattias.ronnblom@ericsson.com> wrote:
>>
>> Add the RTE_EVENT_DEV_CAP_IMPLICIT_RELEASE_DISABLE capability to the
>> DSW event device.
>>
>> This feature may be used by an EAL thread to pull more work from the
>> work scheduler, without giving up the option to forward events
>> originating from a previous dequeue batch. This in turn allows an EAL
>> thread to be productive while waiting for a hardware accelerator to
>> complete some operation.
>>
>> Prior to this change, DSW didn't make any distinction between
>> RTE_EVENT_OP_FORWARD and RTE_EVENT_OP_NEW type events, other than that
>> new events would be backpressured earlier.
>>
>> After this change, DSW tracks the number of released events (i.e.,
>> events of type RTE_EVENT_OP_FORWARD and RTE_EVENT_OP_RELEASE) that has
>> been enqueued.
>>
>> For efficiency reasons, DSW does not track the identity of individual
>> events. This in turn implies that a certain stage in the flow
>> migration process, DSW must wait for all pending releases (on the
>> migration source port, only) to be received from the application, to
>> assure that no event pertaining to any of the to-be-migrated flows are
>> being processed.
>>
>> With this change, DSW starts making a distinction between forward and
>> new type events for credit allocation purposes. Only RTE_EVENT_OP_NEW
>> events needs credits. All events marked as RTE_EVENT_OP_FORWARD must
>> have a corresponding dequeued event from a previous dequeue batch.
>>
>> Flow migration for flows on RTE_SCHED_TYPE_PARALLEL queues remains
>> unaffected by this change.
>>
>> A side-effect of the tweaked DSW migration logic is that the migration
>> latency is reduced, regardless if implicit release is enabled or not.
>>
>> Another side-effect is that migrated flows are now not processed
>> during any part of the migration procedure. An upside of this change
>> it reduces the load of the overloaded port. A downside is it
>> introduces slightly more jitter for the migrated flows.
>>
>> This patch is contains various minor refactorings, improved
>> formatting, fixed spelling, and the removal of unnessary memory
>> barriers.
> 
> Move changelog after ---
> 

I never remember where it should go, so I checked an old patch of mine, 
were I also got it wrong...

Anyway, thanks.

>>
>> v3:
>>   * Fix broken RTE_ASSERT()s. (Jerin Jacob)
>>
>> v2:
>>    * Remove redundant memory barriers.
>>    * Discontinue processing of migrated flows throughout the migration
>>      procedure. This is a part of a fix to address a reordering issue
>>      v1 of this patch introduced.
>>    * Added entry in the release notes.
>>    * Fix spelling issues in commit message.
>>
>> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>> ---
>>   doc/guides/rel_notes/release_24_07.rst |   7 +
>>   drivers/event/dsw/dsw_evdev.c          |   8 +-
>>   drivers/event/dsw/dsw_evdev.h          |   7 +-
>>   drivers/event/dsw/dsw_event.c          | 405 ++++++++++++++-----------
>>   4 files changed, 254 insertions(+), 173 deletions(-)
>>
>> diff --git a/doc/guides/rel_notes/release_24_07.rst b/doc/guides/rel_notes/release_24_07.rst
>> index a69f24cf99..706cc71212 100644
>> --- a/doc/guides/rel_notes/release_24_07.rst
>> +++ b/doc/guides/rel_notes/release_24_07.rst
>> @@ -24,6 +24,13 @@ DPDK Release 24.07
>>   New Features
>>   ------------
>>
>> +* **Updated the DSW event device.**
>> +
>> +  * Added support for ``RTE_EVENT_DEV_CAP_IMPLICIT_RELEASE_DISABLE``,
>> +    allowing applications to take on new tasks without having completed
>> +    (released) the previous event batch. This in turn facilities DSW
>> +    use alongside high-latency look-aside hardware accelerators.
>> +
>>   .. This section should contain new features added in this release.
>>      Sample format:
> 
> Update should be here(after the template).
> 
> 
> Fixed above issues and applied to dpdk-next-eventdev/for-main. Thanks