On Fri, 25 Sep 2020 13:29:00 +0200
Lorenzo Bianconi <lorenzo.bianc...@redhat.com> wrote:
> >
> > On Fri, 25 Sep 2020 12:01:32 +0200
> > Lorenzo Bianconi <lore...@kernel.org> wrote:
> >
> > > Try to recycle the xdp tx buffer into the in-irq page_pool cache if
> > > mvneta_txq_bufs_free is executed in the NAPI context.
> >
> > NACK - I don't think this is safe. That is also why I named the
> > function postfix rx_napi. The page pool->alloc.cache is associated
> > with the drivers RX-queue. The xdp_frame's that gets freed could be
> > coming from a remote driver that use page_pool. This remote drivers
> > RX-queue processing can run concurrently on a different CPU, than this
> > drivers TXQ-cleanup.
>
> ack, right. What about if we do it just XDP_TX use case? Like:
>
> if (napi && buf->type == MVNETA_TYPE_XDP_TX)
> xdp_return_frame_rx_napi(buf->xdpf);
> else
> xdp_return_frame(buf->xdpf);
>
> In this way we are sure the packet is coming from local page_pool.
Yes, that case XDP_TX should be safe.
> >
> > If you want to speedup this, I instead suggest that you add a
> > xdp_return_frame_bulk API.
>
> I will look at it
Great!
Notice that bulk return should be easy/obvious in most drivers, as they
(like mvneta in mvneta_txq_bufs_free()) have a loop that process
several TXQ completions.
I did a quick tests on mlx5 with xdp_redirect_map and perf report shows
__xdp_return calls at the top#1 overhead.
# Overhead CPU Symbol
# ........ ... ....................................
#
8.46% 003 [k] __xdp_return
6.41% 003 [k] dma_direct_map_page
4.65% 003 [k] bpf_xdp_redirect_map
4.58% 003 [k] dma_direct_unmap_page
4.04% 003 [k] xdp_do_redirect
3.53% 003 [k] __page_pool_put_page
3.27% 003 [k] dma_direct_sync_single_for_cpu
2.63% 003 [k] dev_map_enqueue
2.28% 003 [k] page_pool_refill_alloc_cache
1.69% 003 [k] bq_enqueue.isra.0
1.15% 003 [k] _raw_spin_lock
0.92% 003 [k] xdp_return_frame
Thus, there will be a benefit from implementing a bulk return. Also
for your XDP_TX case, as the overhead in __xdp_return also exist for
rx_napi variant.
> > > Signed-off-by: Lorenzo Bianconi <lore...@kernel.org>
> > > ---
> > > drivers/net/ethernet/marvell/mvneta.c | 11 +++++++----
> > > 1 file changed, 7 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/net/ethernet/marvell/mvneta.c
> > > b/drivers/net/ethernet/marvell/mvneta.c
> > > index 14df3aec285d..646fbf4ed638 100644
> > > --- a/drivers/net/ethernet/marvell/mvneta.c
> > > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > > @@ -1831,7 +1831,7 @@ static struct mvneta_tx_queue
> > > *mvneta_tx_done_policy(struct mvneta_port *pp,
> > > /* Free tx queue skbuffs */
> > > static void mvneta_txq_bufs_free(struct mvneta_port *pp,
> > > struct mvneta_tx_queue *txq, int num,
> > > - struct netdev_queue *nq)
> > > + struct netdev_queue *nq, bool napi)
> > > {
> > > unsigned int bytes_compl = 0, pkts_compl = 0;
> > > int i;
> > > @@ -1854,7 +1854,10 @@ static void mvneta_txq_bufs_free(struct
> > > mvneta_port *pp,
> > > dev_kfree_skb_any(buf->skb);
> > > } else if (buf->type == MVNETA_TYPE_XDP_TX ||
> > > buf->type == MVNETA_TYPE_XDP_NDO) {
> > > - xdp_return_frame(buf->xdpf);
> > > + if (napi)
> > > + xdp_return_frame_rx_napi(buf->xdpf);
> > > + else
> > > + xdp_return_frame(buf->xdpf);
> > > }
> > > }
> > >
> > > @@ -1872,7 +1875,7 @@ static void mvneta_txq_done(struct mvneta_port *pp,
> > > if (!tx_done)
> > > return;
> > >
> > > - mvneta_txq_bufs_free(pp, txq, tx_done, nq);
> > > + mvneta_txq_bufs_free(pp, txq, tx_done, nq, true);
> > >
> > > txq->count -= tx_done;
> > >
> > > @@ -2859,7 +2862,7 @@ static void mvneta_txq_done_force(struct
> > > mvneta_port *pp,
> > > struct netdev_queue *nq = netdev_get_tx_queue(pp->dev, txq->id);
> > > int tx_done = txq->count;
> > >
> > > - mvneta_txq_bufs_free(pp, txq, tx_done, nq);
> > > + mvneta_txq_bufs_free(pp, txq, tx_done, nq, false);
> > >
> > > /* reset txq */
> > > txq->count = 0;
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
