Re: [dpdk-dev] [PATCH] ethdev: add lock-less txq capability flag

[Thomas Monjalon <thomas@monjalon.net>]

27/04/2017 13:00, Jerin Jacob:
> -----Original Message-----
> > Date: Mon, 24 Apr 2017 14:34:59 +0200
> > From: Thomas Monjalon <thomas@monjalon.net>
> > To: Jerin Jacob <jerin.jacob@caviumnetworks.com>
> > Cc: dev@dpdk.org, bruce.richardson@intel.com, harry.van.haaren@intel.com,
> >  hemant.agrawal@nxp.com, gage.eads@intel.com, nipun.gupta@nxp.com,
> >  santosh.shukla@caviumnetworks.com
> > Subject: Re: [dpdk-dev]  [PATCH] ethdev: add lock-less txq capability flag
> > 
> > 21/04/2017 14:22, Jerin Jacob:
> > > if this flag is advertised by a PMD, Multiple threads can
> > > invoke rte_eth_tx_burst() concurrently on the same tx queue
> > > without SW lock. This is an HW feature found in some NICs
> > > and useful in the following use cases if HW supports it.
> > 
> > Which hardware supports it?
> 
> Cavium OCTEONTX Packet transmission HW block(PKO).
> 
> > 
> > [...]
> > > --- a/lib/librte_ether/rte_ethdev.h
> > > +++ b/lib/librte_ether/rte_ethdev.h
> > > +#define DEV_TX_OFFLOAD_TXQ_MT_LOCKFREE	0x00004000
> > > +/**< Multiple threads can invoke rte_eth_tx_burst() concurrently on the
> > > same + * tx queue without SW lock.
> > > + */
> > 
> > Why TXQ in the name? DEV_TX_OFFLOAD_MT_LOCKFREE would be enough.
> 
> OK
> 
> > I wonder whether "lock free" wording is confusing because
> > the locks are probably handled in HW.
> 
> Yes. Another reason why it possible because HW is not using ring like scheme(head and tail pointers)
> for Tx. "lock free" wording is more from software perspective.
> 
> > I think the good wording is "offloaded multi-thread capability",
> > maybe with a naming like DEV_TX_OFFLOAD_MT.
> 
> I think SW lock free is the capability here.IMO, it better to reflect the
> capability in the name(DEV_TX_OFFLOAD_MT_LOCKFREE).
> 
> > 
> > Anyway we should reference this flag in rte_eth_tx_burst()
> > and give more details in doc/guides/prog_guide/poll_mode_drv.rst.
> 
> OK. Will address in v2.
> 
> > 
> > Should we wait a first hardware PoC to add this flag?
> 
> If we are in agreement for method expose this feature through capability
> flag then should we really need to wait for driver implementation to
> accept the patch? Thoughts ?
> This flag has impact on how we handle the even dev applications if HW support available.
> We are in the process of up-streaming OCTEONTX ethdev driver, but there
> are few thing like with external pool manager and eventdev integration
> needs to be sorted out cleanly before that.
> 
> > Candidate for 17.08?

Any news of a v2?