Milton Miller wrote:
On May 18, 2007, at 12:11 PM, David Acker wrote:
Kok, Auke wrote:
First impression just came in: It seems RX performance is dropped to
10mbit. TX is unaffected and runs at 94mbit/tcp, but RX the new code
seems to misbehave and fluctuate, dropping below 10mbit after a few
netperf runs and staying there...
ideas?
I found the problem. Another casualty of working with two different
kernels at once...arg.
The blank rfd needs to have its el-bit clear now. Here is the new and
improved patch.
On the ARM, their is a race condition between software allocating a
new receive
buffer and hardware writing into a buffer. The two race on touching
the last
Receive Frame Descriptor (RFD). It has its el-bit set and its next
link equal
to 0. When hardware encounters this buffer it attempts to write data
to it
and then update Status Word bits and Actual Count in the RFD. At the
same time
software may try to clear the el-bit and set the link address to a new
buffer.
Since the entire RFD is once cache-line, the two write operations can
collide. This can lead to the receive unit stalling or freed receive
buffers
getting written to.
The fix is to set the el-bit on and the size to 0 on the next to last
buffer
in the chain. When the hardware encounters this buffer it stops and
does
not write to it at all. The hardware issues an RNR interrupt with the
receive unit in the No Resources state. When software allocates
buffers,
it can update the tail of the list because it knows the hardware will
stop
at the buffer before it. Once it has a new next to last buffer
prepared,
it can clear the el-bit and set the size on the previous one. The
race on
this buffer is safe since the link already points to a valid next
buffer.
If the hardware sees the el-bit cleared without the size set, it will
move on to the next buffer and complete that one in error. If it sees
the size set but the el-bit still set, it will complete that buffer
and then RNR interrupt and wait.
Signed-off-by: David Acker <[EMAIL PROTECTED]>
This patch doesn't apply. It appears white space damaged somewhere:
(1) blank lines in diff are empty not <space>
(2) unchanged lines starting with tab are <space><space><tab>
After fixing the above I still get:
patching file drivers/net/e100.c
Hunk #1 FAILED at 285.
Hunk #4 FAILED at 1749.
Hunk #8 FAILED at 1865.
Hunk #10 succeeded at 1965 with fuzz 1.
Hunk #11 succeeded at 1982 with fuzz 1.
3 out of 14 hunks FAILED -- saving rejects to file
drivers/net/e100.c.rej
although I haven't figured out what is wrong.
Proceeding with the review:
Coding style:
(1) if body on seperate line.
(2) space after if before (
(3) The other enums in this driver are not ALL_CAPS
(4) This driver doesn't do CONSTANT != value but value != enum
(see nic->mac for examples)
I sent Milton my copy of this patch which has these style issues corrected and
applies cleanly to a recent git tree. If anyone else specifically wants a copy
let me know.
Auke
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