RE: [PATCH net-next 3/3] net: stmmac: Introducing support for Page Pool

[Jose Abreu]

From: Jon Hunter <jonathanh@xxxxxxxxxx>
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@xxxxxxxxxxxx>
> > Cc: Joao Pinto <jpinto@xxxxxxxxxxxx>
> > Cc: David S. Miller <davem@xxxxxxxxxxxxx>
> > Cc: Giuseppe Cavallaro <peppe.cavallaro@xxxxxx>
> > Cc: Alexandre Torgue <alexandre.torgue@xxxxxx>
> > Cc: Maxime Coquelin <mcoquelin.stm32@xxxxxxxxx>
> > Cc: Maxime Ripard <maxime.ripard@xxxxxxxxxxx>
> > Cc: Chen-Yu Tsai <wens@xxxxxxxx>
> > ---
> >  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