Message-ID: <20040415012536.61202.qmail@web12505.mail.yahoo.com>
Date: Wed, 14 Apr 2004 18:25:36 -0700 (PDT)
From: ZI ZHOU <zhouzi@yahoo.com>
Subject: HELP ! Why my dev->hard_start_xmit get called three times for one ping packet?
To: linux-kernel@vger.kernel.org
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Hi,

I've written a ethernet device driver based on 2.6.4
sis190.c, and I am testing it on my 2.4.25 machine. I
am currently testing the transmit part and couldn't
figure out the scenorio I've seen. Can someone shed
some light PLEASE !

After I configure the ethernet interface(it's a PCI
card plugged in my debian PC), I run command ' ping -c
1 192.168.0.100', (the interface is configured with IP
address 192.168.0.35), I used smartbit to look at the
wire and found 3 ping packets. From the debugging
info, I can see dev->hard_start_xmit is called three
times, the DMA engine seems to be acting correctly,
and each time hard_start_xmit is invoked the skb
address is different. How can this happen? Could it be
sth related to tx timeout? I am not very clear about
what happens between IP send and dev->hard_start_xmit
besides knowing there is a queue for skb, and if
device is busy, the skb will be re-queued? Can someone
give me some idea about how the driver communicate
with the upper layer software about the status of its
transmit ? There used to be tbusy I remember, but I've
lost track of what happen there after.

Btw, I run different number of ping packets, here is
some result, Haven't been able to make sense out of it
yet.

ping -c 1/2/3  -> recv 3 packets
ping -c 4/5/6  -> recv 6 packets
ping -c 7      -> recv 8 packets

Thanks & your help is greatly appreciated !

Zi

 
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