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Date: Wed, 15 Mar 2017 18:07:16 -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 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;
+ }
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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