Re: [dpdk-dev] [PATCH v2 4/4] net/mlx5: engage free on completion queue

[Slava Ovsiienko <viacheslavo@mellanox.com>]

> -----Original Message-----
> From: Thomas Monjalon <thomas@monjalon.net>
> Sent: Friday, January 10, 2020 11:34
> To: Slava Ovsiienko <viacheslavo@mellanox.com>
> Cc: Ferruh Yigit <ferruh.yigit@intel.com>; dev@dpdk.org; Matan Azrad
> <matan@mellanox.com>; Raslan Darawsheh <rasland@mellanox.com>; Ori
> Kam <orika@mellanox.com>
> Subject: Re: [dpdk-dev] [PATCH v2 4/4] net/mlx5: engage free on completion
> queue
> 
> 10/01/2020 10:28, Slava Ovsiienko:
> > From: Thomas Monjalon <thomas@monjalon.net>
> > > 09/01/2020 17:22, Slava Ovsiienko:
> > > > From: Ferruh Yigit <ferruh.yigit@intel.com>
> > > > > On 1/9/2020 3:27 PM, Slava Ovsiienko wrote:
> > > > > > From: Ferruh Yigit <ferruh.yigit@intel.com>
> > > > > >> On 1/9/2020 10:56 AM, Viacheslav Ovsiienko wrote:
> > > > > >>> +		assert(ci != txq->cq_pi);
> > > > > >>> +		assert((txq->fcqs[ci & txq->cqe_m] >> 16) == cqe-
> > > > > >>> wqe_counter);
> > > > > >>
> > > > > >> And same comments on these as previous patches, we spend some
> > > > > >> effort to remove the 'rte_panic' from drivers, this is almost same
> thing.
> > > > > >>
> > > > > >> I think a driver shouldn't decide to exit whole application,
> > > > > >> it's effect should be limited to the driver.
> > > > > >>
> > > > > >> Assert is useful for debug and during development, but not
> > > > > >> sure having them in the production code.
> > > > > >
> > > > > > IIRC, "assert" is standard C function. Compiled only if there
> > > > > > is no NDEBUG
> > > > > defined.
> > > > > > So, assert does exactly what you are saying - provide the
> > > > > > debug break not allowing the bug to evolve. And no this break
> > > > > > in production
> > > code.
> > > > > >
> > > > >
> > > > > Since mlx driver is using NDEBUG defined, what you said is right
> > > > > indeed. But why not using RTE_ASSERT to be consistent with rest.
> > > > > There is a specific config option to control assert
> > > > > (RTE_ENABLE_ASSERT) and anyone using it will get different
> > > > > behavior with
> > > mlx5.
> > > >
> > > > We have the dedicated option to control mlx5 debug:
> > > > CONFIG_RTE_ENABLE_ASSERT controls the whole DPDK.
> > >
> > > No, it controls the whole DPDK except mlx PMDs.
> > >
> > > > CONFIG_RTE_LIBRTE_MLX5_DEBUG controls NDEBUG for mlx5
> > > >
> > > > From my practice - I switch the mlx5 debug option (in the process
> > > > of the debugging/testing datapath and checking the resulting
> > > > performance, by directly defining NDEBUG in mlx5.h and not
> > > > reconfiguring/rebuilding the
> > > entire DPDK), this fine grained option seems to be useful.
> > >
> > > I don't like having mlx PMDs behave differently.
> > > It make things difficult for newcomers.
> > > And with meson, such options are cleaned up.
> >
> > Do you mean we should eliminate NDEBUG usage and convert it to some
> explicit "MLX5_NDEBUG"
> > (and convert "assert" to "MLX5_ASSERT") ?
> 
> I mean we should use RTE_ASSERT in mlx5, as it is already done in some files.
> 
This would make not possible to engage asserts  in mlx5 module only.
It is a question of structuring/layering, not "different behavior".
As for me - it is very nice to have fine grained debug control option,
and I use this feature actively, it just saves my time. Also, it seems 
these options are implemented in many other PMDs
(with its own xxx_ASSERTs).

With best regards, Slava