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

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Date:   Fri, 11 Oct 2019 17:58:47 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.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) 

Hi Ilias,

yes, right. We need to account pending xdp buffer len on tx side.

> 
> 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.

If this introduce a performance penalty we can just account netdev tx_bytes
directly (maybe it is ugly)

Regards,
Lorenzo

> 
> 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
> > > 

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