Re: [RFC PATCH 0/4] ethdev new offloads API

[Thomas Monjalon <thomas@monjalon.net>]

28/08/2017 07:00, Jerin Jacob:
> From: Shahaf Shuler <shahafs@mellanox.com>
> > Friday, August 25, 2017 1:32 PM, Jerin Jacob:
> > > >
> > > > The new API does not have an equivalent for the below Tx flags:
> > > >
> > > > * ETH_TXQ_FLAGS_NOREFCOUNT
> > > > * ETH_TXQ_FLAGS_NOMULTMEMP
> > > 
> > > IMO, it make sense to keep those flags as PMD optimization if an application
> > > does not need reference count and multi mempool in the application.
> > > As example, An non trivial application like l3fwd does not need both of them.
> > 
> > The l3fwd application is yet another simple example from DPDK tree. Am not sure that a complete vRouter/vSwitch implementation is with the same characteristics.
> 
> But not all dpdk applications are complete vRouter/vSwitch implementation.
> 
> > Moreover, I think the fact there is an application which is able to use it is not enough.  IMO there needs to be some basic functionality always provided by the PMDs and not controlled by flags.
> > For example, let's say we have an application which always sends the mbufs with the same ol_flags, or even with the same length.
> 
> Does ETH_TXQ_FLAGS_NOREFCOUNT comes in same category like mbuf->ol_flags?
> 
> > Will it make sense to add more flags to control it?
> > Will it makes sense to run RFC2544 benchmark with testpmd io forwarding with those flags? 
> > 
> > If the answer is yes, maybe those flags (and others to follow) belong on different location on ethdev. However for sure they are not offloads.
> 
> I am not sure about the reason for opting out mempool related flags.
> In the context of HW assisted external mempool managers, Enabling reference count is an offload
> from Ethernet device.
> For example, with external HW assisted mempool, ethdev driver needs to
> have different way of forming TXQ descriptor in case if reference count
> is enabled(as, in the case of HW assisted mempool managers, bu default,
> HW frees the packet on send)
> 
> I am fine with moving the flags to some where else if it is make sense to you.But
> from PMD optimization perspective, I think it is important have these flags.

Why not.
Please Jerin, could you work on moving these settings in a new API?
We can have a function to enable such optimizations.
However I am not sure ethdev is the right place as these hints apply
to any mbuf.
Other related question: what happens if other libraries manipulate
these mbufs with special optimization hints? Should they be aware?