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

[Slava Ovsiienko <viacheslavo@mellanox.com>]

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@intel.com>
> Sent: Thursday, January 9, 2020 17:44
> To: Slava Ovsiienko <viacheslavo@mellanox.com>; dev@dpdk.org
> Cc: Matan Azrad <matan@mellanox.com>; Raslan Darawsheh
> <rasland@mellanox.com>; Ori Kam <orika@mellanox.com>; Thomas
> Monjalon <thomas@monjalon.net>
> Subject: Re: [dpdk-dev] [PATCH v2 4/4] net/mlx5: engage free on completion
> queue
> 
> On 1/9/2020 3:27 PM, Slava Ovsiienko wrote:
> >> -----Original Message-----
> >> From: Ferruh Yigit <ferruh.yigit@intel.com>
> >> Sent: Thursday, January 9, 2020 17:19
> >> To: Slava Ovsiienko <viacheslavo@mellanox.com>; dev@dpdk.org
> >> Cc: Matan Azrad <matan@mellanox.com>; Raslan Darawsheh
> >> <rasland@mellanox.com>; Ori Kam <orika@mellanox.com>; Thomas
> Monjalon
> >> <thomas@monjalon.net>
> >> Subject: Re: [dpdk-dev] [PATCH v2 4/4] net/mlx5: engage free on
> >> completion queue
> >>
> >> On 1/9/2020 10:56 AM, Viacheslav Ovsiienko wrote:
> >>> The free on completion queue keeps the indices of elts array, all
> >>> mbuf stored below this index should be freed on arrival of normal
> >>> send completion. In debug version it also contains an index of
> >>> completed transmitting descriptor (WQE) to check queues
> synchronization.
> >>>
> >>> Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
> >>> Acked-by: Matan Azrad <matan@mellanox.com>
> >>
> >> <...>
> >>
> >>> @@ -2108,17 +2108,18 @@ enum mlx5_txcmp_code {
> >>>  			/*
> >>>  			 * We are going to fetch all entries with
> >>>  			 * MLX5_CQE_SYNDROME_WR_FLUSH_ERR status.
> >>> +			 * The send queue is supposed to be empty.
> >>>  			 */
> >>>  			++ci;
> >>> +			txq->cq_pi = ci;
> >>> +			last_cqe = NULL;
> >>>  			continue;
> >>>  		}
> >>>  		/* Normal transmit completion. */
> >>> +		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.

OK, to summarize (after discussions with Ferruh and Thomas):
1. assert/NDEBUG in mlx5 should be fixed
2 in mlx5 assert should be replaced by MLX5_ASSERT macro, it provides "in-development" assert control if needed
3. mlx5 PMDs local debug configuration option will be removed from global build configuration 
(it is absent in meson build now, and as makefile is subject to drop - this option will not be supported anymore)
4. The patch in subject ("net/mlx5: engage free on completion queue") is not related to bullets 1-3 and
   should be accepted to Upstream, and the is the claimed commitment from my side to provide
  the dedicated patch for 1-3.

With best regards, Slava