Date:	Mon, 19 Feb 2007 17:29:20 -0500
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	pcnet32@...izon.net
Cc:	netdev@...r.kernel.org
Subject: Re: Re: Strange connection slowdown on pcnet32

On Mon, Feb 19, 2007 at 05:18:45PM -0500, Lennart Sorensen wrote:
> On Mon, Feb 19, 2007 at 03:11:36PM -0500, Lennart Sorensen wrote:
> > I have been poking at things with firescope to see if the MAC is
> > actually writing to system memory or not.
> > 
> > The entry that it gets stuch on is _always_ entry 0 in the rx_ring.
> > There does not appear to be any exceptions to this.  
> > 
> > Here is my firescope (slightly modified for this purpose) dump of the
> > rx_ring of eth1:
> > 
> > Descriptor:Address: /--base---\ /buf\ /sta\ /-message-\ /reserved-\
> >           :       : |         | |len| |tus| | length  | |         |
> > RXdesc[00]:6694000: 12 18 5f 05 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[01]:6694010: 12 78 15 05 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[02]:6694020: 12 a0 52 06 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[03]:6694030: 12 f8 c2 04 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[04]:6694040: 12 70 15 05 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[05]:6694050: 12 e8 37 05 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[06]:6694060: 12 e0 37 05 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[07]:6694070: 12 e8 d5 04 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[08]:6694080: 12 e0 d5 04 fa f9 40 03 ee 05 00 00 00 00 00 00
> > RXdesc[09]:6694090: 12 d8 d1 05 fa f9 40 03 46 00 00 00 00 00 00 00
> > RXdesc[10]:66940a0: 12 d0 d1 05 fa f9 40 03 4e 00 00 00 00 00 00 00
> > RXdesc[11]:66940b0: 12 d8 02 05 fa f9 10 03 40 00 00 00 00 00 00 00
> > RXdesc[12]:66940c0: 12 d0 02 05 fa f9 40 03 46 00 00 00 00 00 00 00
> > RXdesc[13]:66940d0: 12 38 58 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[14]:66940e0: 12 30 58 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[15]:66940f0: 12 78 2c 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[16]:6694100: 12 a0 58 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[17]:6694110: 12 b0 04 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[18]:6694120: 12 b8 04 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[19]:6694130: 12 70 2c 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[20]:6694140: 12 f8 56 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[21]:6694150: 12 c8 29 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[22]:6694160: 12 20 03 05 fa f9 00 80 ee 05 00 00 00 00 00 00
> > RXdesc[23]:6694170: 12 60 4c 05 fa f9 00 80 87 05 00 00 00 00 00 00
> > RXdesc[24]:6694180: 12 98 53 05 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[25]:6694190: 12 b0 cc 04 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[26]:66941a0: 12 a8 3f 05 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[27]:66941b0: 12 58 e8 04 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[28]:66941c0: 12 b0 4d 06 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[29]:66941d0: 12 38 ef 04 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[30]:66941e0: 12 98 1f 05 fa f9 00 80 40 00 00 00 00 00 00 00
> > RXdesc[31]:66941f0: 12 28 f1 04 fa f9 00 80 40 00 00 00 00 00 00 00
> > 
> > I only ever see entry 0 as status 0080 (0x8000 which is owned by mac),
> > and this is while the driver is checking entry 0 every time it tries to
> > check for any waiting packets.
> > 
> > Running tcpdump while pinging gives the interesting result that some
> > packets are ariving out of order making it seem like the driver is
> > processing the packets out of order.  Perhaps the driver is wrong to be
> > looking at entry 0, and should be looking at entry 1 and is hence stuck
> > until the whole receive ring has been filled again?
> > 
> > 15:06:04.112812 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 1
> > 15:06:05.119799 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 2
> > 15:06:05.120159 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 2
> > 15:06:05.127045 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 1
> > 15:06:06.119862 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 3
> > 15:06:07.119921 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 4
> > 15:06:08.119994 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 5
> > 15:06:08.426400 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 3
> > 15:06:08.427915 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 4
> > 15:06:08.429033 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 5
> > 15:06:09.120053 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 6
> > 15:06:10.120109 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 7
> > 15:06:10.705332 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 6
> > 15:06:10.707258 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 7
> > 15:06:11.120175 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 8
> > 15:06:12.120233 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 9
> > 15:06:13.120297 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 10
> > 15:06:14.120359 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 11
> > 15:06:14.120737 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 11
> > 15:06:14.127064 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 8
> > 15:06:14.127700 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 9
> > 15:06:14.128268 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 10
> > 15:06:15.120426 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 12
> > 15:06:16.120484 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 13
> > 15:06:16.120840 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 13
> > 15:06:16.129476 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 12
> > 15:06:17.120551 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 14
> > 15:06:17.615429 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 14
> > 15:06:18.120612 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 15
> > 15:06:19.120672 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 16
> > 15:06:19.748981 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 15
> > 15:06:19.749976 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 16
> > 15:06:20.120738 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 17
> > 15:06:21.120799 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 18
> > 15:06:22.120859 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 19
> > 15:06:23.120926 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 20
> > 15:06:24.120985 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 21
> > 15:06:24.881809 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 17
> > 15:06:24.882287 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 18
> > 15:06:24.882578 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 19
> > 15:06:24.883347 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 20
> > 15:06:24.884158 IP 10.128.10.1 > 10.128.10.254: icmp 64: echo reply seq 21
> > 15:06:25.129659 IP 10.128.10.254 > 10.128.10.1: icmp 64: echo request seq 22
> > 
> > Does anyone see any reason why the driver would get into such a state
> > after a pile of traffic in a row?  So far I have only seen it when NAPI
> > is enabled, so I have to assume so far that it makes a difference to it.
> 
> With more beating of the driver, I have managed to see it fail in places
> other than descriptor 0.  It is as if the MAC doesn't transfer the
> descriptor to the system memory, although I am not yet sure if there is
> packet loss involved involving retransmision or not.
> 
> I tried making this change as a test:
> 
>   static int pcnet32_rx(struct net_device *dev, int quota)
>   {
>           struct pcnet32_private *lp = dev->priv;
>           int entry = lp->cur_rx & lp->rx_mod_mask;
> +         int nextentry = (lp->cur_rx+1) & lp->rx_mod_mask;
>           struct pcnet32_rx_head *rxp = &lp->rx_ring[entry];
> +         struct pcnet32_rx_head *nextrxp = &lp->rx_ring[nextentry];
>           int npackets = 0;
> 
> +         /* Check for confused MAC and resync if necesary */
> +         if ((short)le16_to_cpu(rxp->status) < 0 && (short)le16_to_cpu(nextrxp->status) >= 0) {
> +                 entry = (++lp->cur_rx) & lp->rx_mod_mask;
> +                 rxp = &lp->rx_ring[entry];
> +                 printk("%s: rx_ring bugfix on entry %d\n",dev->name,entry);
> +         }
> 
>           /* If we own the next entry, it's a new packet. Send it up. */
>           while (quota > npackets && (short)le16_to_cpu(rxp->status) >= 0) {
>                   pcnet32_rx_entry(dev, lp, rxp, entry);
>                   npackets += 1;
>                   /*
>                    * The docs say that the buffer length isn't touched, but Andrew
>                    * Boyd of QNX reports that some revs of the 79C965 clear it.
>                    */
>                   rxp->buf_length = le16_to_cpu(2 - PKT_BUF_SZ);
>                   wmb();  /* Make sure owner changes after others are visible */
>                   rxp->status = le16_to_cpu(0x8000);
>                   entry = (++lp->cur_rx) & lp->rx_mod_mask;
>                   rxp = &lp->rx_ring[entry];
>           }
> 
>           return npackets;
>   }
> 
> Now this really can't be a solution.  It still occationally gets "stuck"
> for a short time, but with this change it manages to recover again but
> it does seem to be hitting by printk once in a while.  I am starting to
> wonder of the PCI transfers are failing once in a while.  I still can't
> figure out what NAPI is doing different unless some of the pcnet32_rx
> code should be run with interrupts disabled and isn't in NAPI mode.
> 
> eth1: rx_ring bugfix on entry 28
> eth1: rx_ring bugfix on entry 15
> eth1: rx_ring bugfix on entry 31
> eth1: rx_ring bugfix on entry 2
> eth1: rx_ring bugfix on entry 23
> eth1: rx_ring bugfix on entry 25
> eth1: rx_ring bugfix on entry 2
> eth1: rx_ring bugfix on entry 21
> eth1: rx_ring bugfix on entry 24
> eth1: rx_ring bugfix on entry 27
> eth1: rx_ring bugfix on entry 28
> eth1: rx_ring bugfix on entry 23
> eth1: rx_ring bugfix on entry 11
> eth1: rx_ring bugfix on entry 28
> eth1: rx_ring bugfix on entry 27
> eth1: rx_ring bugfix on entry 24
> eth1: rx_ring bugfix on entry 28
> eth1: rx_ring bugfix on entry 17

I just noticed, it seems almost all these problems occour right at the
start of transfers when the tcp window size is still being worked out
for the connection speed, and I am seeing the error count go up in
ifconfig for the port when it happens too.  Is it possible for an error
to get flagged in a receive descriptor without the owner bit being
updated?

--
Len Sorensen
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