On Fri, Mar 19, 2021 at 12:10 PM Maciej Fijalkowski
<maciej.fijalkow...@intel.com> wrote:
>
> On Fri, Mar 19, 2021 at 10:44:10AM +0100, Magnus Karlsson wrote:
> > From: Magnus Karlsson <magnus.karls...@intel.com>
> >
> > Fix so that single packets are received immediately instead of in
> > batches of 8. If you sent 1 pss to a system, you received 8 packets
>
> pps?
Arghh, yes it should be pps, i.e. packets per second. I wonder what pss is?
> > every 8 seconds instead of 1 packet every second. The problem behind
> > this was that the work_done reporting from the Tx part of the driver
> > was broken. The work_done reporting in i40e controls not only the
> > reporting back to the napi logic but also the setting of the interrupt
> > throttling logic. When Tx or Rx reports that it has more to do,
> > interrupts are throttled or coalesced and when they both report that
> > they are done, interrupts are armed right away. If the wrong work_done
> > value is returned, the logic will start to throttle interrupts in a
> > situation where it should have just enabled them. This leads to the
> > undesired batching behavior seen in user-space.
> >
> > Fix this by returning the correct boolean value from the Tx xsk
> > zero-copy path. Return true if there is nothing to do or if we got
> > fewer packets to process than we asked for. Return false if we got as
> > many packets as the budget since there might be more packets we can
> > process.
> >
> > Fixes: 3106c580fb7c ("i40e: Use batched xsk Tx interfaces to increase
> > performance")
> > Reported-by: Sreedevi Joshi <sreedevi.jo...@intel.com>
> > Signed-off-by: Magnus Karlsson <magnus.karls...@intel.com>
>
> Acked-by: Maciej Fijalkowski <maciej.fijalkow...@intel.com>
>
> > ---
> > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > index fc32c5019b0f..12ca84113587 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > @@ -471,7 +471,7 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring,
> > unsigned int budget)
> >
> > nb_pkts = xsk_tx_peek_release_desc_batch(xdp_ring->xsk_pool, descs,
> > budget);
> > if (!nb_pkts)
> > - return false;
> > + return true;
> >
> > if (xdp_ring->next_to_use + nb_pkts >= xdp_ring->count) {
> > nb_processed = xdp_ring->count - xdp_ring->next_to_use;
> > @@ -488,7 +488,7 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring,
> > unsigned int budget)
> >
> > i40e_update_tx_stats(xdp_ring, nb_pkts, total_bytes);
> >
> > - return true;
> > + return nb_pkts < budget;
> > }
> >
> > /**
> >
> > base-commit: c79a707072fe3fea0e3c92edee6ca85c1e53c29f
> > --
> > 2.29.0
> >
