Hello.
I've attached to this mail a patch for the FEC driver
on the Motorola MPC8xx embedded CPU.
This patch includes both a bug fix, and a new PHYter implementation.
Symptom
---------
I was experiencing problems of "transmission timeout" when heavily
loading the network (throughput tests), particularly when the board
was wired to a 10MBits link (but I could also reproduce it on 100Mbits
using the packet sockets). The user process was then "held" by the IP
stack, I had no choice but to kill it.
Bug description
-----------------
When, in rare cases, the ring buffer became full, the driver was stopping
the network queue, which is OK. But, it did not set a flag to restart
the queue in the transmission interrupt service routine.
Bug fix
---------
I only had to set this flag, at the same time the network queue was stopped
(already wrapped in a spin lock).
Supplement:
PHYter implementation
-----------------------
My board uses the NS chip model DP83843BVJE, for which I filled out the
needed structures.
However, I could not test the PHYter interrupt since it is not wired to the
PPC on our board
(but it is enabled in this patch). I had to code a polling routine (not
included in this patch).
It might be a good idea to move all these implementations outside of
"fec.c".
It might be also useful to choose the supported models through the kernel
configuration.
Perhaps I will work on that during the next weeks...
By the way, who is maintaining that part (MPC8xx, MPC82xx) of the kernel?
Other issue
-------------
I have another problem I will have to address. I'm experiencing a strange
behaviour
in the response time when I 'ping flood' my board.
Through the 10Mbits, everything works fine, the average response time is
468us,
with realist minimum and maximum values.
> round-trip min/avg/max/mdev = 0.458/0.468/0.600/0.029 ms
But, through the 100Mbits, the response time ranges from 0.26ms to 10ms,
and an average of about 5ms, always different from test to test.
> round-trip min/avg/max/mdev = 0.265/6.764/10.311/4.512 ms
Strangely, the board is not running anything but bash.
If a start 'top' with a refresh period of 1 second, I get a lower average,
but still the same min and max.
> round-trip min/avg/max/mdev = 0.264/0.583/10.018/1.421 ms
If I start an NFS copy of a big file, the maximum gets down to 2ms.
The maximum of 10ms sounds like the timer tick.
Since it is working well in 10Mbps and not in 100Mbps,
can I suspect a problem with the Ethernet driver?
Thank you for your time.
--------------------------------------------
Jean-Denis Boyer, B.Eng., Technical Leader
Mediatrix Telecom Inc.
4229 Garlock Street
Sherbrooke (Québec)
J1L 2C8 CANADA
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This archive was generated by hypermail 2b29 : Sun Apr 15 2001 - 21:00:14 EST