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Date: Thu, 5 Nov 2020 08:19:11 +0100
From: Magnus Karlsson <magnus.karlsson@...il.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: "Karlsson, Magnus" <magnus.karlsson@...el.com>,
Björn Töpel <bjorn.topel@...el.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Network Development <netdev@...r.kernel.org>,
Jonathan Lemon <jonathan.lemon@...il.com>,
bpf <bpf@...r.kernel.org>, jeffrey.t.kirsher@...el.com,
anthony.l.nguyen@...el.com,
Maciej Fijalkowski <maciejromanfijalkowski@...il.com>,
intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [PATCH bpf-next 6/6] i40e: use batched xsk Tx interfaces to
increase performance
On Thu, Nov 5, 2020 at 12:12 AM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> On Wed, Nov 04, 2020 at 03:09:02PM +0100, Magnus Karlsson wrote:
> > From: Magnus Karlsson <magnus.karlsson@...el.com>
> >
> > Use the new batched xsk interfaces for the Tx path in the i40e driver
> > to improve performance. On my machine, this yields a throughput
> > increase of 4% for the l2fwd sample app in xdpsock. If we instead just
> > look at the Tx part, this patch set increases throughput with above
> > 20% for Tx.
> >
> > Note that I had to explicitly loop unroll the inner loop to get to
> > this performance level, by using a pragma. It is honored by both clang
> > and gcc and should be ignored by versions that do not support
> > it. Using the -funroll-loops compiler command line switch on the
> > source file resulted in a loop unrolling on a higher level that
> > lead to a performance decrease instead of an increase.
> >
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> > ---
> > drivers/net/ethernet/intel/i40e/i40e_ethtool.c | 2 +-
> > drivers/net/ethernet/intel/i40e/i40e_main.c | 4 +-
> > drivers/net/ethernet/intel/i40e/i40e_txrx.c | 14 ++-
> > drivers/net/ethernet/intel/i40e/i40e_txrx.h | 3 +-
> > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 127 ++++++++++++++++++-------
> > 5 files changed, 110 insertions(+), 40 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> > index 26ba1f3..dc34867 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> > @@ -2025,7 +2025,7 @@ static int i40e_set_ringparam(struct net_device *netdev,
> > */
> > tx_rings[i].desc = NULL;
> > tx_rings[i].rx_bi = NULL;
> > - err = i40e_setup_tx_descriptors(&tx_rings[i]);
> > + err = i40e_setup_tx_descriptors(&tx_rings[i], false);
> > if (err) {
> > while (i) {
> > i--;
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c b/drivers/net/ethernet/intel/i40e/i40e_main.c
> > index 4f8a2154..c93774a 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> > @@ -3030,13 +3030,13 @@ static int i40e_vsi_setup_tx_resources(struct i40e_vsi *vsi)
> > int i, err = 0;
> >
> > for (i = 0; i < vsi->num_queue_pairs && !err; i++)
> > - err = i40e_setup_tx_descriptors(vsi->tx_rings[i]);
> > + err = i40e_setup_tx_descriptors(vsi->tx_rings[i], false);
> >
> > if (!i40e_enabled_xdp_vsi(vsi))
> > return err;
> >
> > for (i = 0; i < vsi->num_queue_pairs && !err; i++)
> > - err = i40e_setup_tx_descriptors(vsi->xdp_rings[i]);
> > + err = i40e_setup_tx_descriptors(vsi->xdp_rings[i], true);
>
> One last suggestion: I think that you could just call ring_is_xdp(tx_ring)
> within i40e_setup_tx_descriptors() and based on that allocate the
> xsk_descs array, instead of parametrizing the function. At the time of
> setting up tx descs the I40E_TXR_FLAGS_XDP flag is already set.
>
> I think this would be a cleaner way of doing it.
Yes, good suggestion. Will do that.
> >
> > return err;
> > }
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > index d43ce13..3e13e0e 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > @@ -676,6 +676,8 @@ void i40e_free_tx_resources(struct i40e_ring *tx_ring)
> > i40e_clean_tx_ring(tx_ring);
> > kfree(tx_ring->tx_bi);
> > tx_ring->tx_bi = NULL;
> > + kfree(tx_ring->xsk_descs);
> > + tx_ring->xsk_descs = NULL;
> >
> > if (tx_ring->desc) {
> > dma_free_coherent(tx_ring->dev, tx_ring->size,
> > @@ -1259,10 +1261,11 @@ void i40e_clean_programming_status(struct i40e_ring *rx_ring, u64 qword0_raw,
> > /**
> > * i40e_setup_tx_descriptors - Allocate the Tx descriptors
> > * @tx_ring: the tx ring to set up
> > + * @xdp_ring: true if this is an XDP Tx ring
> > *
> > * Return 0 on success, negative on error
> > **/
> > -int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring)
> > +int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring, bool xdp_ring)
> > {
> > struct device *dev = tx_ring->dev;
> > int bi_size;
> > @@ -1277,6 +1280,13 @@ int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring)
> > if (!tx_ring->tx_bi)
> > goto err;
> >
> > + if (xdp_ring) {
> > + tx_ring->xsk_descs = kcalloc(I40E_MAX_NUM_DESCRIPTORS, sizeof(*tx_ring->xsk_descs),
> > + GFP_KERNEL);
> > + if (!tx_ring->xsk_descs)
> > + goto err;
> > + }
> > +
> > u64_stats_init(&tx_ring->syncp);
> >
> > /* round up to nearest 4K */
> > @@ -1300,6 +1310,8 @@ int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring)
> > return 0;
> >
> > err:
> > + kfree(tx_ring->xsk_descs);
> > + tx_ring->xsk_descs = NULL;
> > kfree(tx_ring->tx_bi);
> > tx_ring->tx_bi = NULL;
> > return -ENOMEM;
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> > index 2feed92..628d5d7 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> > @@ -389,6 +389,7 @@ struct i40e_ring {
> > struct i40e_channel *ch;
> > struct xdp_rxq_info xdp_rxq;
> > struct xsk_buff_pool *xsk_pool;
> > + struct xdp_desc *xsk_descs; /* For storing descriptors in the AF_XDP ZC path */
> > } ____cacheline_internodealigned_in_smp;
> >
> > static inline bool ring_uses_build_skb(struct i40e_ring *ring)
> > @@ -451,7 +452,7 @@ bool i40e_alloc_rx_buffers(struct i40e_ring *rxr, u16 cleaned_count);
> > netdev_tx_t i40e_lan_xmit_frame(struct sk_buff *skb, struct net_device *netdev);
> > void i40e_clean_tx_ring(struct i40e_ring *tx_ring);
> > void i40e_clean_rx_ring(struct i40e_ring *rx_ring);
> > -int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring);
> > +int i40e_setup_tx_descriptors(struct i40e_ring *tx_ring, bool xdp_ring);
> > int i40e_setup_rx_descriptors(struct i40e_ring *rx_ring);
> > void i40e_free_tx_resources(struct i40e_ring *tx_ring);
> > void i40e_free_rx_resources(struct i40e_ring *rx_ring);
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > index eabe1a3..515d856 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> > @@ -383,6 +383,78 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
> > return failure ? budget : (int)total_rx_packets;
> > }
> >
> > +static void i40e_xmit_pkt(struct i40e_ring *xdp_ring, struct xdp_desc *desc,
> > + unsigned int *total_bytes)
> > +{
> > + struct i40e_tx_desc *tx_desc;
> > + dma_addr_t dma;
> > +
> > + dma = xsk_buff_raw_get_dma(xdp_ring->xsk_pool, desc->addr);
> > + xsk_buff_raw_dma_sync_for_device(xdp_ring->xsk_pool, dma, desc->len);
> > +
> > + tx_desc = I40E_TX_DESC(xdp_ring, xdp_ring->next_to_use++);
> > + tx_desc->buffer_addr = cpu_to_le64(dma);
> > + tx_desc->cmd_type_offset_bsz = build_ctob(I40E_TX_DESC_CMD_ICRC | I40E_TX_DESC_CMD_EOP,
> > + 0, desc->len, 0);
> > +
> > + *total_bytes += desc->len;
> > +}
> > +
> > +/* This value should match the pragma below. Why 4? It is strictly
> > + * empirical. It seems to be a good compromise between the advantage
> > + * of having simultaneous outstanding reads to the DMA array that can
> > + * hide each others latency and the disadvantage of having a larger
> > + * code path.
> > + */
> > +#define PKTS_PER_BATCH 4
> > +
> > +static void i40e_xmit_pkt_batch(struct i40e_ring *xdp_ring, struct xdp_desc *desc,
> > + unsigned int *total_bytes)
> > +{
> > + u16 ntu = xdp_ring->next_to_use;
> > + struct i40e_tx_desc *tx_desc;
> > + dma_addr_t dma;
> > + u32 i;
> > +
> > +#pragma GCC unroll 4
> > + for (i = 0; i < PKTS_PER_BATCH; i++) {
> > + dma = xsk_buff_raw_get_dma(xdp_ring->xsk_pool, desc[i].addr);
> > + xsk_buff_raw_dma_sync_for_device(xdp_ring->xsk_pool, dma, desc[i].len);
> > +
> > + tx_desc = I40E_TX_DESC(xdp_ring, ntu++);
> > + tx_desc->buffer_addr = cpu_to_le64(dma);
> > + tx_desc->cmd_type_offset_bsz = build_ctob(I40E_TX_DESC_CMD_ICRC |
> > + I40E_TX_DESC_CMD_EOP,
> > + 0, desc[i].len, 0);
> > +
> > + *total_bytes += desc[i].len;
> > + }
> > +
> > + xdp_ring->next_to_use = ntu;
> > +}
> > +
> > +static void i40e_fill_tx_hw_ring(struct i40e_ring *xdp_ring, struct xdp_desc *descs, u32 nb_pkts,
> > + unsigned int *total_bytes)
> > +{
> > + u32 batched, leftover, i;
> > +
> > + batched = nb_pkts & ~(PKTS_PER_BATCH - 1);
> > + leftover = nb_pkts & (PKTS_PER_BATCH - 1);
> > + for (i = 0; i < batched; i += PKTS_PER_BATCH)
> > + i40e_xmit_pkt_batch(xdp_ring, &descs[i], total_bytes);
> > + for (i = batched; i < batched + leftover; i++)
> > + i40e_xmit_pkt(xdp_ring, &descs[i], total_bytes);
> > +}
> > +
> > +static void i40e_set_rs_bit(struct i40e_ring *xdp_ring)
> > +{
> > + u16 ntu = xdp_ring->next_to_use ? xdp_ring->next_to_use - 1 : xdp_ring->count - 1;
> > + struct i40e_tx_desc *tx_desc;
> > +
> > + tx_desc = I40E_TX_DESC(xdp_ring, ntu);
> > + tx_desc->cmd_type_offset_bsz |= (I40E_TX_DESC_CMD_RS << I40E_TXD_QW1_CMD_SHIFT);
> > +}
> > +
> > /**
> > * i40e_xmit_zc - Performs zero-copy Tx AF_XDP
> > * @xdp_ring: XDP Tx ring
> > @@ -392,45 +464,30 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
> > **/
> > static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
> > {
> > - unsigned int sent_frames = 0, total_bytes = 0;
> > - struct i40e_tx_desc *tx_desc = NULL;
> > - struct xdp_desc desc;
> > - dma_addr_t dma;
> > -
> > - while (budget-- > 0) {
> > - if (!xsk_tx_peek_desc(xdp_ring->xsk_pool, &desc))
> > - break;
> > -
> > - dma = xsk_buff_raw_get_dma(xdp_ring->xsk_pool, desc.addr);
> > - xsk_buff_raw_dma_sync_for_device(xdp_ring->xsk_pool, dma,
> > - desc.len);
> > -
> > - tx_desc = I40E_TX_DESC(xdp_ring, xdp_ring->next_to_use);
> > - tx_desc->buffer_addr = cpu_to_le64(dma);
> > - tx_desc->cmd_type_offset_bsz =
> > - build_ctob(I40E_TX_DESC_CMD_ICRC
> > - | I40E_TX_DESC_CMD_EOP,
> > - 0, desc.len, 0);
> > -
> > - sent_frames++;
> > - total_bytes += desc.len;
> > -
> > - xdp_ring->next_to_use++;
> > - if (xdp_ring->next_to_use == xdp_ring->count)
> > - xdp_ring->next_to_use = 0;
> > + struct xdp_desc *descs = xdp_ring->xsk_descs;
> > + u32 nb_pkts, nb_processed = 0;
> > + unsigned int total_bytes = 0;
> > +
> > + nb_pkts = xsk_tx_peek_release_desc_batch(xdp_ring->xsk_pool, descs, budget);
> > + if (!nb_pkts)
> > + return false;
> > +
> > + if (xdp_ring->next_to_use + nb_pkts >= xdp_ring->count) {
> > + nb_processed = xdp_ring->count - xdp_ring->next_to_use;
> > + i40e_fill_tx_hw_ring(xdp_ring, descs, nb_processed, &total_bytes);
> > + xdp_ring->next_to_use = 0;
> > }
> >
> > - if (tx_desc) {
> > - /* Request an interrupt for the last frame and bump tail ptr. */
> > - tx_desc->cmd_type_offset_bsz |= (I40E_TX_DESC_CMD_RS <<
> > - I40E_TXD_QW1_CMD_SHIFT);
> > - i40e_xdp_ring_update_tail(xdp_ring);
> > + i40e_fill_tx_hw_ring(xdp_ring, &descs[nb_processed], nb_pkts - nb_processed,
> > + &total_bytes);
> >
> > - xsk_tx_release(xdp_ring->xsk_pool);
> > - i40e_update_tx_stats(xdp_ring, sent_frames, total_bytes);
> > - }
> > + /* Request an interrupt for the last frame and bump tail ptr. */
> > + i40e_set_rs_bit(xdp_ring);
> > + i40e_xdp_ring_update_tail(xdp_ring);
> > +
> > + i40e_update_tx_stats(xdp_ring, nb_pkts, total_bytes);
> >
> > - return !!budget;
> > + return true;
> > }
> >
> > /**
> > --
> > 2.7.4
> >
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