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Date: Wed, 15 Mar 2017 18:10:55 -0700
From: Eric Dumazet <eric.dumazet@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>,
"David S . Miller" <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
Tariq Toukan <tariqt@...lanox.com>,
Saeed Mahameed <saeedm@...lanox.com>,
Willem de Bruijn <willemb@...gle.com>,
Alexei Starovoitov <ast@...nel.org>,
Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH v2 net-next] mlx4: Better use of order-0 pages in RX path
On Wed, 2017-03-15 at 18:07 -0700, Eric Dumazet wrote:
> On Wed, 2017-03-15 at 16:06 -0700, Alexei Starovoitov wrote:
>
> > yes. and we have 'xdp_tx_full' counter for it that we monitor.
> > When tx ring and mtu are sized properly, we don't expect to see it
> > incrementing at all. This is something in our control. 'Our' means
> > humans that setup the environment.
> > 'cache empty' condition is something ephemeral. Packets will be dropped
> > and we won't have any tools to address it. These packets are real
> > people requests. Any drop needs to be categorized.
> > Like there is 'rx_fifo_errors' counter that mlx4 reports when
> > hw is dropping packets before they reach the driver. We see it
> > incrementing depending on the traffic pattern though overall Mpps
> > through the nic is not too high and this is something we
> > actively investigating too.
>
>
> This all looks nice, except that current mlx4 driver does not have a
> counter of failed allocations.
>
> You are asking me to keep some inexistent functionality.
>
> Look in David net tree :
>
> mlx4_en_refill_rx_buffers()
> ...
> if (mlx4_en_prepare_rx_desc(...))
> break;
>
>
> So in case of memory pressure, mlx4 stops working and not a single
> counter is incremented/reported.
>
> So I guess your supervision was not really tested.
>
> Just to show you what you are asking, here is a diff against latest
> version.
>
> You want to make sure a fresh page is there before calling XDP program.
>
> Is it really what you want ?
>
> drivers/net/ethernet/mellanox/mlx4/en_rx.c | 38 +++++++++++++----------------
> 1 file changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index cc41f2f145541b469b52e7014659d5fdbb7dac68..e5ef8999087b52705faf083c94cde439aab9e2b7 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -793,10 +793,24 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
> if (xdp_prog) {
> struct xdp_buff xdp;
> struct page *npage;
> - dma_addr_t ndma, dma;
> + dma_addr_t dma;
> void *orig_data;
> u32 act;
>
> + /* Make sure we have one page ready to replace this one, per Alexei request */
> + if (unlikely(!ring->page_cache.index)) {
> + npage = mlx4_alloc_page(priv, ring,
> + &ring->page_cache.buf[0].dma,
> + numa_mem_id(),
> + GFP_ATOMIC | __GFP_MEMALLOC);
> + if (!npage) {
> + /* replace this by a new ring->rx_alloc_failed++
> + */
> + ring->xdp_drop++;
> + goto next;
> + }
> + ring->page_cache.buf[0].page = npage;
Plus a missing :
ring->page_cache.index = 1;
> + }
> dma = frags[0].dma + frags[0].page_offset;
> dma_sync_single_for_cpu(priv->ddev, dma,
> priv->frag_info[0].frag_size,
> @@ -820,29 +834,13 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
> case XDP_PASS:
> break;
> case XDP_TX:
> - /* Make sure we have one page ready to replace this one */
> - npage = NULL;
> - if (!ring->page_cache.index) {
> - npage = mlx4_alloc_page(priv, ring,
> - &ndma, numa_mem_id(),
> - GFP_ATOMIC | __GFP_MEMALLOC);
> - if (!npage) {
> - ring->xdp_drop++;
> - goto next;
> - }
> - }
> if (likely(!mlx4_en_xmit_frame(ring, frags, dev,
> length, cq->ring,
> &doorbell_pending))) {
> - if (ring->page_cache.index) {
> - u32 idx = --ring->page_cache.index;
> + u32 idx = --ring->page_cache.index;
>
> - frags[0].page = ring->page_cache.buf[idx].page;
> - frags[0].dma = ring->page_cache.buf[idx].dma;
> - } else {
> - frags[0].page = npage;
> - frags[0].dma = ndma;
> - }
> + frags[0].page = ring->page_cache.buf[idx].page;
> + frags[0].dma = ring->page_cache.buf[idx].dma;
> frags[0].page_offset = XDP_PACKET_HEADROOM;
> goto next;
> }
>
>
>
>
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