netdev - Re: [PATCH v1 6/7] net: mvneta: Don't use GRO on Armada 3720

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Date:   Thu, 9 Aug 2018 20:08:32 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Marek Behún <marek.behun@....cz>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Tomas Hlavacek <tomas.hlavacek@....cz>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH v1 6/7] net: mvneta: Don't use GRO on Armada 3720

On Thu, 9 Aug 2018 19:27:55 +0800 Jisheng Zhang wrote:

> Hi,
> 
> On Thu, 9 Aug 2018 12:40:41 +0800 Jisheng Zhang wrote:
> 
> > + more people
> > 
> > On Wed,  8 Aug 2018 17:27:05 +0200 Marek Behún wrote:
> >   
> > > For some reason on Armada 3720 boards (EspressoBin and Turris Mox) the
> > > networking driver behaves weirdly when using napi_gro_receive.
> > > 
> > > For example downloading a big file from a local network (low ping) is
> > > fast, but when downloading from a remote server (higher ping), the
> > > download speed is at first high but drops rapidly to almost nothing or
> > > absolutely nothing.    
> > 
> > We also met this issue on some berlin platforms. I tried to fix the bug,
> > but no clue so far.
> >   
> > > 
> > > This is fixed when using netif_receive_skb instead of napi_gro_receive.    
> > 
> > This is a workaround. The good news is this workaround also fixes the issue
> > we saw on berlin.
> >   
> > > 
> > > Signed-off-by: Marek Behun <marek.behun@....cz>
> > > Cc: Russell King - ARM Linux <linux@...linux.org.uk>
> > > Cc: netdev@...r.kernel.org
> > > 
> > > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > > index 0ad2f3f7da85..27f3017d94c5 100644
> > > --- a/drivers/net/ethernet/marvell/mvneta.c
> > > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > > @@ -1959,7 +1959,10 @@ static int mvneta_rx_swbm(struct mvneta_port *pp, int rx_todo,
> > >  
> > >  			skb->protocol = eth_type_trans(skb, dev);
> > >  			mvneta_rx_csum(pp, rx_status, skb);
> > > -			napi_gro_receive(&port->napi, skb);
> > > +			if (pp->neta_armada3700)
> > > +				netif_receive_skb(skb);
> > > +			else
> > > +				napi_gro_receive(&port->napi, skb);  
> 
> I think I found the root cause, if neta_armada3700 is true, the port got from
> this_cpu_ptr(pp->ports) is invalid, this is bug... I'll cook a patch for this

correct it as:

the port's(port is got from this_cpu_ptr(pp->ports) napi is invalid.

Patch is sent out. Could you please try?

Per my test, it solves the issue we saw on berlin.

> 
> Thanks
> 
> > >  
> > >  			rcvd_pkts++;
> > >  			rcvd_bytes += rx_bytes;
> > > @@ -2001,7 +2004,10 @@ static int mvneta_rx_swbm(struct mvneta_port *pp, int rx_todo,
> > >  
> > >  		mvneta_rx_csum(pp, rx_status, skb);
> > >  
> > > -		napi_gro_receive(&port->napi, skb);
> > > +		if (pp->neta_armada3700)
> > > +			netif_receive_skb(skb);
> > > +		else
> > > +			napi_gro_receive(&port->napi, skb);
> > >  	}
> > >  
> > >  	if (rcvd_pkts) {    
> >   
>