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Date: Fri, 25 Sep 2020 15:05:43 +0200
From: Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To: Jesper Dangaard Brouer <brouer@...hat.com>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>,
Network Development <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Eelco Chaudron <echaudro@...hat.com>,
thomas.petazzoni@...tlin.com
Subject: Re: [PATCH net-next] net: mvneta: try to use in-irq pp cache in
mvneta_txq_bufs_free
> On Fri, 25 Sep 2020 13:29:00 +0200
> Lorenzo Bianconi <lorenzo.bianconi@...hat.com> wrote:
>
> > >
> > > On Fri, 25 Sep 2020 12:01:32 +0200
> > > Lorenzo Bianconi <lorenzo@...nel.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.
ack, I will post a v2 limiting the xdp_return_frame_rx_napi just for XDP_TX
use-case and then I will look at implementing a xdp bulk return.
Regards,
Lorenzo
>
>
> > > > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.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
>
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