Subject: Re: Realtek 8139 problem on 486.

From: Nikolai Zhubr <[email-masked]>
Date: Mon, 31 May 2021 19:53:52 +0300

Hi all,

31.05.2021 2:17, Nikolai Zhubr:
[...]
> However indeed, it seems a problem was introduced with a rework of
> interrupt handling (rtl8139_interrupt) in 2.6.3, because I have already
> pushed all other differences from 2.6.3 to 2.6.2 and it still keeps
> working fine.
> My resulting minimized diff is still ~300 lines, it is too big and
> complicated to be usefull to post here as is.

Some more input.

I was able to minimize the problematic diff to basically one screenfull, 
it is quite comprehencable now, and I'm including it below. It is the 
change in status/event handling due to a switch to NAPI that intruduced 
the problem.
Now, in some more detailed tests, I observe that _receiving_ still works 
fine. It is _sending_ that suffers, and apparently, only when trying to 
send a lot at a time. In such case I see these warnings:

NETDEV WATCHDOG: eth0: transmit timed out
eth0: link up, 100Mbps, full-duplex, lpa 0xC5E1

It looks like the queue of tx frames somehow gets messed up.

The essential diff fragment:
================================================
  	dev->open = rtl8139_open;
  	dev->hard_start_xmit = rtl8139_start_xmit;
+	dev->poll = rtl8139_poll;
  	dev->weight = 64;
  	dev->stop = rtl8139_close;
  	dev->get_stats = rtl8139_get_stats;
@@ -2015,7 +2010,7 @@
  			tp->stats.rx_bytes += pkt_size;
  			tp->stats.rx_packets++;

-			netif_rx (skb);
+			netif_receive_skb (skb);
  		} else {
  			if (net_ratelimit())
  				printk (KERN_WARNING
@@ -2138,10 +2133,8 @@
  	u16 status, ackstat;
  	int link_changed = 0; /* avoid bogus "uninit" warning */
  	int handled = 0;
-	int boguscnt = max_interrupt_work;

  	spin_lock (&tp->lock);
-	do {
  	status = RTL_R16 (IntrStatus);

  	/* shared irq? */
@@ -2169,8 +2162,14 @@
  	if (ackstat)
  		RTL_W16 (IntrStatus, ackstat);

-	if (netif_running (dev) && (status & RxAckBits))
-		rtl8139_rx (dev, tp, 1000000000);
+	/* Receive packets are processed by poll routine.
+	   If not running start it now. */
+	if (status & RxAckBits){
+		if (netif_rx_schedule_prep(dev)) {
+			RTL_W16_F (IntrMask, rtl8139_norx_intr_mask);
+			__netif_rx_schedule (dev);
+		}
+	}

  	/* Check uncommon events with one test. */
  	if (unlikely(status & (PCIErr | PCSTimeout | RxUnderrun | RxErr)))
@@ -2182,16 +2181,6 @@
  		if (status & TxErr)
  			RTL_W16 (IntrStatus, TxErr);
  	}
-	boguscnt--;
-	} while (boguscnt > 0);
-
================================================

Thank you,

Regards,
Nikolai