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Message-ID: <57effc14-afed-51c8-9926-686d1cdea803@intel.com>
Date: Mon, 22 Jun 2020 18:00:29 -0700
From: "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To: Magnus Karlsson <magnus.karlsson@...el.com>, bjorn.topel@...el.com,
intel-wired-lan@...ts.osuosl.org, jeffrey.t.kirsher@...el.com
Cc: maciejromanfijalkowski@...il.com, maciej.fijalkowski@...el.com,
netdev@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH net-next 1/2] i40e: optimize AF_XDP Tx
completion path
On 6/22/2020 6:21 AM, Magnus Karlsson wrote:
> Improve the performance of the AF_XDP zero-copy Tx completion
> path. When there are no XDP buffers being sent using XDP_TX or
> XDP_REDIRECT, we do not have go through the SW ring to clean up any
> entries since the AF_XDP path does not use these. In these cases, just
> fast forward the next-to-use counter and skip going through the SW
> ring. The limit on the maximum number of entries to complete is also
> removed since the algorithm is now O(1). To simplify the code path, the
> maximum number of entries to complete for the XDP path is therefore
> also increased from 256 to 512 (the default number of Tx HW
> descriptors). This should be fine since the completion in the XDP path
> is faster than in the SKB path that has 256 as the maximum number.
>
> This patch provides around 4% throughput improvement for the l2fwd
> application in xdpsock on my machine.
>
> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> ---
> drivers/net/ethernet/intel/i40e/i40e_txrx.c | 1 +
> drivers/net/ethernet/intel/i40e/i40e_txrx.h | 1 +
> drivers/net/ethernet/intel/i40e/i40e_xsk.c | 34 ++++++++++++++++-------------
> 3 files changed, 21 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> index f9555c8..0ce9d1e 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> @@ -3538,6 +3538,7 @@ static int i40e_xmit_xdp_ring(struct xdp_frame *xdpf,
> */
> smp_wmb();
>
> + xdp_ring->xdp_tx_active++;
> i++;
> if (i == xdp_ring->count)
> i = 0;
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> index 5c25597..c16fcd9 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
> @@ -371,6 +371,7 @@ struct i40e_ring {
> /* used in interrupt processing */
> u16 next_to_use;
> u16 next_to_clean;
> + u16 xdp_tx_active;
>
> u8 atr_sample_rate;
> u8 atr_count;
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index 7276580..c8cd6a6 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -378,6 +378,7 @@ 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 i40e_tx_buffer *tx_bi;
> bool work_done = true;
> @@ -408,6 +409,9 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
> | I40E_TX_DESC_CMD_EOP,
> 0, desc.len, 0);
>
> + sent_frames++;
> + total_bytes += tx_bi->bytecount;
> +
> xdp_ring->next_to_use++;
> if (xdp_ring->next_to_use == xdp_ring->count)
> xdp_ring->next_to_use = 0;
> @@ -420,6 +424,7 @@ static bool i40e_xmit_zc(struct i40e_ring *xdp_ring, unsigned int budget)
> i40e_xdp_ring_update_tail(xdp_ring);
>
> xsk_umem_consume_tx_done(xdp_ring->xsk_umem);
> + i40e_update_tx_stats(xdp_ring, sent_frames, total_bytes);
> }
>
> return !!budget && work_done;
> @@ -434,6 +439,7 @@ static void i40e_clean_xdp_tx_buffer(struct i40e_ring *tx_ring,
> struct i40e_tx_buffer *tx_bi)
> {
> xdp_return_frame(tx_bi->xdpf);
> + tx_ring->xdp_tx_active--;
> dma_unmap_single(tx_ring->dev,
> dma_unmap_addr(tx_bi, dma),
> dma_unmap_len(tx_bi, len), DMA_TO_DEVICE);
> @@ -450,24 +456,23 @@ static void i40e_clean_xdp_tx_buffer(struct i40e_ring *tx_ring,
> bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi,
> struct i40e_ring *tx_ring, int napi_budget)
napi_budget is not used. so the 3rd arg can be removed
> {
> - unsigned int ntc, total_bytes = 0, budget = vsi->work_limit;
> - u32 i, completed_frames, frames_ready, xsk_frames = 0;
> + unsigned int ntc, budget = vsi->work_limit;
> struct xdp_umem *umem = tx_ring->xsk_umem;
> + u32 i, completed_frames, xsk_frames = 0;
> u32 head_idx = i40e_get_head(tx_ring);
> bool work_done = true, xmit_done;
work_done is no longer required
> struct i40e_tx_buffer *tx_bi;
>
> if (head_idx < tx_ring->next_to_clean)
> head_idx += tx_ring->count;
> - frames_ready = head_idx - tx_ring->next_to_clean;
> + completed_frames = head_idx - tx_ring->next_to_clean;
>
> - if (frames_ready == 0) {
> + if (completed_frames == 0)
> goto out_xmit;
> - } else if (frames_ready > budget) {
> - completed_frames = budget;
> - work_done = false;
> - } else {
> - completed_frames = frames_ready;
> +
> + if (likely(!tx_ring->xdp_tx_active)) {
> + xsk_frames = completed_frames;
> + goto skip;
> }
>
> ntc = tx_ring->next_to_clean;
> @@ -475,18 +480,18 @@ bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi,
> for (i = 0; i < completed_frames; i++) {
> tx_bi = &tx_ring->tx_bi[ntc];
>
> - if (tx_bi->xdpf)
> + if (tx_bi->xdpf) {
> i40e_clean_xdp_tx_buffer(tx_ring, tx_bi);
> - else
> + tx_bi->xdpf = NULL;
> + } else {
> xsk_frames++;
> -
> - tx_bi->xdpf = NULL;
> - total_bytes += tx_bi->bytecount;
> + }
>
> if (++ntc >= tx_ring->count)
> ntc = 0;
> }
>
> +skip:
> tx_ring->next_to_clean += completed_frames;
> if (unlikely(tx_ring->next_to_clean >= tx_ring->count))
> tx_ring->next_to_clean -= tx_ring->count;
> @@ -495,7 +500,6 @@ bool i40e_clean_xdp_tx_irq(struct i40e_vsi *vsi,
> xsk_umem_complete_tx(umem, xsk_frames);
>
> i40e_arm_wb(tx_ring, vsi, budget);
I guess budget here should be replaced with completed_frames
> - i40e_update_tx_stats(tx_ring, completed_frames, total_bytes);
>
> out_xmit:
> if (xsk_umem_uses_need_wakeup(tx_ring->xsk_umem))
>
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