[dpdk-dev] [RFC 01/15] eventdev: make driver interface as internal

[Mattias Rönnblom]

On 2021-08-24 09:43, Mattias Rönnblom wrote:
> On 2021-08-23 21:40, pbhagavatula at marvell.com wrote:
>> From: Pavan Nikhilesh <pbhagavatula at marvell.com>
>>
>> Mark all the driver specific functions as internal, remove
>> `rte` prefix from `struct rte_eventdev_ops`.
>> Remove experimental tag from internal functions.
>> Remove `eventdev_pmd.h` from non-internal header files.
>>
> Is the enqueue/dequeue shortcut still worth the trouble? Considering the
> size of this patch set, it seems to be a lot of trouble to handle this
> special case.
>
>

I had a quick look at this, using an overhead measurement benchmark for 
DSW. Depending on compiler version and details of the test program's 
structure, the gains ranged from modest to non-existent. In some 
scenarios, the inline versions even performed more poorly than a 
function call proper. This was on a Intel Skylake and static DPDK linking.


The dev and port lookup are essentially a very short pointer chase, and 
in case the dev table and the dev struct itself is not in a close cache, 
significant stalls may occur. For most applications they will be in L1 
though, I imagine. The inline version should give the compiler some 
freedom to generate the appropriate loads earlier. If you insert a 
compiler barrier before the rte_event_*() call, the inline version seem 
to have no gains at all.


Did anyone else attempt to quantify the performance gains with keeping 
these functions as inline?


/M