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SubjectRE: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool
Date
From: Jon Hunter <jonathanh@nvidia.com>
Date: Jul/25/2019, 14:20:07 (UTC+00:00)

>
> On 03/07/2019 11:37, Jose Abreu wrote:
> > Mapping and unmapping DMA region is an high bottleneck in stmmac driver,
> > specially in the RX path.
> >
> > This commit introduces support for Page Pool API and uses it in all RX
> > queues. With this change, we get more stable troughput and some increase
> > of banwidth with iperf:
> > - MAC1000 - 950 Mbps
> > - XGMAC: 9.22 Gbps
> >
> > Signed-off-by: Jose Abreu <joabreu@synopsys.com>
> > Cc: Joao Pinto <jpinto@synopsys.com>
> > Cc: David S. Miller <davem@davemloft.net>
> > Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
> > Cc: Alexandre Torgue <alexandre.torgue@st.com>
> > Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
> > Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> > Cc: Chen-Yu Tsai <wens@csie.org>
> > ---
> > drivers/net/ethernet/stmicro/stmmac/Kconfig | 1 +
> > drivers/net/ethernet/stmicro/stmmac/stmmac.h | 10 +-
> > drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 196 ++++++----------------
> > 3 files changed, 63 insertions(+), 144 deletions(-)
>
> ...
>
> > @@ -3306,49 +3295,22 @@ static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
> > else
> > p = rx_q->dma_rx + entry;
> >
> > - if (likely(!rx_q->rx_skbuff[entry])) {
> > - struct sk_buff *skb;
> > -
> > - skb = netdev_alloc_skb_ip_align(priv->dev, bfsize);
> > - if (unlikely(!skb)) {
> > - /* so for a while no zero-copy! */
> > - rx_q->rx_zeroc_thresh = STMMAC_RX_THRESH;
> > - if (unlikely(net_ratelimit()))
> > - dev_err(priv->device,
> > - "fail to alloc skb entry %d\n",
> > - entry);
> > - break;
> > - }
> > -
> > - rx_q->rx_skbuff[entry] = skb;
> > - rx_q->rx_skbuff_dma[entry] =
> > - dma_map_single(priv->device, skb->data, bfsize,
> > - DMA_FROM_DEVICE);
> > - if (dma_mapping_error(priv->device,
> > - rx_q->rx_skbuff_dma[entry])) {
> > - netdev_err(priv->dev, "Rx DMA map failed\n");
> > - dev_kfree_skb(skb);
> > + if (!buf->page) {
> > + buf->page = page_pool_dev_alloc_pages(rx_q->page_pool);
> > + if (!buf->page)
> > break;
> > - }
> > -
> > - stmmac_set_desc_addr(priv, p, rx_q->rx_skbuff_dma[entry]);
> > - stmmac_refill_desc3(priv, rx_q, p);
> > -
> > - if (rx_q->rx_zeroc_thresh > 0)
> > - rx_q->rx_zeroc_thresh--;
> > -
> > - netif_dbg(priv, rx_status, priv->dev,
> > - "refill entry #%d\n", entry);
> > }
> > - dma_wmb();
> > +
> > + buf->addr = buf->page->dma_addr;
> > + stmmac_set_desc_addr(priv, p, buf->addr);
> > + stmmac_refill_desc3(priv, rx_q, p);
> >
> > rx_q->rx_count_frames++;
> > rx_q->rx_count_frames %= priv->rx_coal_frames;
> > use_rx_wd = priv->use_riwt && rx_q->rx_count_frames;
> >
> > - stmmac_set_rx_owner(priv, p, use_rx_wd);
> > -
> > dma_wmb();
> > + stmmac_set_rx_owner(priv, p, use_rx_wd);
> >
> > entry = STMMAC_GET_ENTRY(entry, DMA_RX_SIZE);
> > }
>
> I was looking at this change in a bit closer detail and one thing that
> stuck out to me was the above where the barrier had been moved from
> after the stmmac_set_rx_owner() call to before.
>
> So I moved this back and I no longer saw the crash. However, then I
> recalled I had the patch to enable the debug prints for the buffer
> address applied but after reverting that, the crash occurred again.
>
> In other words, what works for me is moving the above barrier and adding
> the debug print, which appears to suggest that there is some
> timing/coherency issue here. Anyway, maybe this is clue to what is going
> on?
>
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index a7486c2f3221..2f016397231b 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -3303,8 +3303,8 @@ static inline void stmmac_rx_refill(struct stmmac_priv *priv, u32 queue)
> rx_q->rx_count_frames %= priv->rx_coal_frames;
> use_rx_wd = priv->use_riwt && rx_q->rx_count_frames;
>
> - dma_wmb();
> stmmac_set_rx_owner(priv, p, use_rx_wd);
> + dma_wmb();
>
> entry = STMMAC_GET_ENTRY(entry, DMA_RX_SIZE);
> }
> @@ -3438,6 +3438,10 @@ static int stmmac_rx(struct stmmac_priv *priv, int limit, u32 queue)
> dma_sync_single_for_device(priv->device, buf->addr,
> frame_len, DMA_FROM_DEVICE);
>
> + pr_info("%s: paddr=0x%llx, vaddr=0x%llx, len=%d", __func__,
> + buf->addr, page_address(buf->page),
> + frame_len);
> +
> if (netif_msg_pktdata(priv)) {
> netdev_dbg(priv->dev, "frame received (%dbytes)",
> frame_len);
>
> Cheers
> Jon
>
> --
> nvpublic

Well, I wasn't expecting that :/

Per documentation of barriers I think we should set descriptor fields
and then barrier and finally ownership to HW so that remaining fields
are coherent before owner is set.

Anyway, can you also add a dma_rmb() after the call to
stmmac_rx_status() ?

---
Thanks,
Jose Miguel Abreu
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