netdev - Re: [PATCH net-next 3/3] net/mlx5e: use indirect calls wrapper for the rx packet handler

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Date:   Mon, 03 Jun 2019 11:55:12 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "leon@...nel.org" <leon@...nel.org>
Subject: Re: [PATCH net-next 3/3] net/mlx5e: use indirect calls wrapper for
 the rx packet handler

On Fri, 2019-05-31 at 18:41 +0000, Saeed Mahameed wrote:
> On Fri, 2019-05-31 at 14:53 +0200, Paolo Abeni wrote:
> > We can avoid another indirect call per packet wrapping the rx
> > handler call with the proper helper.
> > 
> > To ensure that even the last listed direct call experience
> > measurable gain, despite the additional conditionals we must
> > traverse before reaching it, I tested reversing the order of the
> > listed options, with performance differences below noise level.
> > 
> > Together with the previous indirect call patch, this gives
> > ~6% performance improvement in raw UDP tput.
> > 
> 
> Nice ! I like it.
> 
> > Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> > ---
> >  drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > index 0fe5f13d07cc..c3752dbe00c8 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
> > @@ -1333,7 +1333,9 @@ int mlx5e_poll_rx_cq(struct mlx5e_cq *cq, int
> > budget)
> >  
> >  		mlx5_cqwq_pop(cqwq);
> >  
> > -		rq->handle_rx_cqe(rq, cqe);
> > +		INDIRECT_CALL_4(rq->handle_rx_cqe,
> > mlx5e_handle_rx_cqe_mpwrq,
> > +				mlx5e_handle_rx_cqe,
> > mlx5e_handle_rx_cqe_rep,
> > +				mlx5e_ipsec_handle_rx_cqe, rq, cqe);
> 
> you missed mlx5i_handle_rx_cqe, anyway don't add INDIRECT_CALL_5 :D
> 
> just replace mlx5e_handle_rx_cqe_rep with mlx5i_handle_rx_cqe, 
> mlx5e_handle_rx_cqe_rep is actually a slow path of switchdev mode.

Thank you! This is exactly the kind of feedback I was looking for! I
hoped some of the options was less relevant than the other, but I do
not know the driver well enough to guess. Also I missed completely
mlx5i_handle_rx_cqe, as you noded.

> Maybe define the list somewhere in en.h where it is visible for every
> one:
> 
> #define MLX5_RX_INDIRECT_CALL_LIST \
> mlx5e_handle_rx_cqe_mpwrq, mlx5e_handle_rx_cqe, mlx5i_handle_rx_cqe,
> mlx5e_ipsec_handle_rx_cqe
> 
> and here:
> INDIRECT_CALL_4(rq->handle_rx_cqe, MLX5_RX_INDIRECT_CALL_LIST, rq,
> cqe);

Will do in v2, unless this patch will be dropped, please see my reply
to patch 2/3.

Thanks,

Paolo