Re: [dpdk-dev] [RFC 19.11 1/2] ethdev: make DPDK core functions non-inline

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jul 30, 2019 at 03:01:00PM +0000, Jerin Jacob Kollanukkaran wrote:
> > -----Original Message----- From: dev <dev-bounces@dpdk.org> On Behalf
> > Of Marcin Zapolski Sent: Tuesday, July 30, 2019 6:20 PM To:
> > dev@dpdk.org Cc: Marcin Zapolski <marcinx.a.zapolski@intel.com>
> > Subject: [dpdk-dev] [RFC 19.11 1/2] ethdev: make DPDK core functions
> > non- inline
> > 
> > Make rte_eth_rx_burst, rte_eth_tx_burst and other static inline ethdev
> > functions not inline. They are referencing DPDK internal structures and
> > inlining forces those structures to be exposed to user applications.
> > 
> > In internal testing with i40e NICs a performance drop of about 2% was
> > observed with testpmd.
> 
> I tested on two class of arm64 machines(Highend and lowend) one has 1.4%
> drop And other one has 3.6% drop.
>
This is with testpmd only right? I'd just point out that we need to
remember that these numbers need to be scaled down appropriately for a
realworld app where IO is only a (hopefully small) proportion of the packet
processing budget. For example, I would expect the ~2% drop we saw in
testpmd to correspond to <0.5% drop in something like OVS.
 
> I second to not expose internal data structure to avoid ABI break.
> 
> IMO, This patch has performance issue due to it is fixing it in simple
> way.
> 
> It is not worth two have function call overhead to call the driver
> function.  Some thoughts below to reduce the performance impact without
> exposing internal structures.
> 
The big concern I have with what you propose is that would involve changing
each and every ethdev driver in DPDK! I'd prefer to make sure that the
impact of this change is actually felt in real-world apps before we start
looking to make such updates across the DPDK codebase.

> And I think, We need to follow the similar mechanism for cryptodev, Eventdev, rawdev
> Etc so bring the common scheme to address this semantics will be use full.
> 
Agreed.

Regards,
/Bruce