netdev - Re: [PATCH net] net: socionext: netsec: fix xdp stats accounting

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Date:   Fri, 11 Oct 2019 18:16:28 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        lorenzo.bianconi@...hat.com
Subject: Re: [PATCH net] net: socionext: netsec: fix xdp stats accounting

On Fri, Oct 11, 2019 at 05:15:03PM +0300, Ilias Apalodimas wrote:
> Hi Lorenzo, 
> 
> On Fri, Oct 11, 2019 at 03:45:38PM +0200, Lorenzo Bianconi wrote:
> > Increment netdev rx counters even for XDP_DROP verdict. Moreover report
> > even tx bytes for xdp buffers (TYPE_NETSEC_XDP_TX or
> > TYPE_NETSEC_XDP_NDO)
> 
> The RX counters work fine. The TX change is causing a panic though and i am
> looking into it since your patch seems harmless. In any case please don't merge
> this yet
> 

Ok i think i know what's going on. 
Our clean TX routine has a netdev_completed_queue(). This is properly accounted
for on netsec_netdev_start_xmit() which calls netdev_sent_queue().

Since the XDP never had support for that you need to account for the extra bytes
in netsec_xdp_queue_one(). That's what triggering the BUG_ON 
(lib/dynamic_queue_limits.c line 27) 

Since netdev_completed_queue() enforces barrier() and in some cases smp_mb() i
think i'd prefer it per function, although it looks uglier. 
Can you send a patch with this call in netsec_xdp_queue_one()? If we cant
measure any performance difference i am fine with adding it in that only.

Thanks
/Ilias

> Thanks
> /Ilias
> 
> > Fixes: ba2b232108d3 ("net: netsec: add XDP support")
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> > just compiled not tested on a real device
> > ---
> >  drivers/net/ethernet/socionext/netsec.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
> > index f9e6744d8fd6..b1c2a79899b3 100644
> > --- a/drivers/net/ethernet/socionext/netsec.c
> > +++ b/drivers/net/ethernet/socionext/netsec.c
> > @@ -252,7 +252,6 @@
> >  #define NETSEC_XDP_CONSUMED      BIT(0)
> >  #define NETSEC_XDP_TX            BIT(1)
> >  #define NETSEC_XDP_REDIR         BIT(2)
> > -#define NETSEC_XDP_RX_OK (NETSEC_XDP_PASS | NETSEC_XDP_TX | NETSEC_XDP_REDIR)
> >  
> >  enum ring_id {
> >  	NETSEC_RING_TX = 0,
> > @@ -661,6 +660,7 @@ static bool netsec_clean_tx_dring(struct netsec_priv *priv)
> >  			bytes += desc->skb->len;
> >  			dev_kfree_skb(desc->skb);
> >  		} else {
> > +			bytes += desc->xdpf->len;
> >  			xdp_return_frame(desc->xdpf);
> >  		}
> >  next:
> > @@ -1030,7 +1030,7 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
> >  
> >  next:
> >  		if ((skb && napi_gro_receive(&priv->napi, skb) != GRO_DROP) ||
> > -		    xdp_result & NETSEC_XDP_RX_OK) {
> > +		    xdp_result) {
> >  			ndev->stats.rx_packets++;
> >  			ndev->stats.rx_bytes += xdp.data_end - xdp.data;
> >  		}
> > -- 
> > 2.21.0
> >