Re: [PATCH] net/mlx5: fix calculating TSO inline size

["Nélio Laranjeiro" <nelio.laranjeiro@6wind.com>]

On Mon, Sep 11, 2017 at 03:17:44PM -0700, Yongseok Koh wrote:
> On Mon, Sep 04, 2017 at 04:01:08PM +0200, Nélio Laranjeiro wrote:
> > Hi Yongseok,
> > 
> > Please see some comments below,
> > 
> > On Thu, Aug 31, 2017 at 09:27:06AM -0700, Yongseok Koh wrote:
> > > Tx descriptor for TSO embeds packet header to be replicated. If Tx inline
> > > is enabled, there could be additional packet data inlined with 4B inline
> > > header ahead. And between the header and additional inlined packet data,
> > > there may be padding to make the inline part aligned to
> > > MLX5_WQE_DWORD_SIZE. In calculating the total size of inlined data, the
> > > size of inline header and padding is missing.
> > > 
> > > Fixes: 3f13f8c23a7c ("net/mlx5: support hardware TSO")
> > > Cc: stable@dpdk.org
> > > 
> > > Signed-off-by: Shahaf Shuler <shahafs@mellanox.com>
> > > Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
> > > ---
> > >  drivers/net/mlx5/mlx5_rxtx.c | 25 +++++++++----------------
> > >  1 file changed, 9 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c
> > > index fe9e7eac0..f89fa40b5 100644
> > > --- a/drivers/net/mlx5/mlx5_rxtx.c
> > > +++ b/drivers/net/mlx5/mlx5_rxtx.c
> > > @@ -524,19 +521,20 @@ mlx5_tx_burst(void *dpdk_txq, struct rte_mbuf **pkts, uint16_t pkts_n)
> > >  		}
> > >  		/* Inline if enough room. */
> > >  		if (inline_en || tso) {
> > > +			uint32_t inl;
> > >  			uintptr_t end = (uintptr_t)
> > >  				(((uintptr_t)txq->wqes) +
> > >  				 (1 << txq->wqe_n) * MLX5_WQE_SIZE);
> > >  			unsigned int inline_room = max_inline *
> > >  						   RTE_CACHE_LINE_SIZE -
> > > -						   (pkt_inline_sz - 2);
> > > +						   (pkt_inline_sz - 2) -
> > > +						   !!tso * sizeof(inl);
> > 
> > Is not it dangerous to assume inl will always be 4 bytes long?  Why not
> > writing the real value instead?
> That was for readability of the code and uint32_t will be always 4bytes. But for
> better readability, it should be 'inline_header' instead of 'inl' though. I'm
> also okay with using "4" as well. Which way do you prefer?

I agree on both, I was not clear enough to explain my thought, if for some
reason the inl moves from uint32_t to uint16_t without touching the sizeof
later, it will cause an issue.

Thanks,

-- 
Nélio Laranjeiro
6WIND