threadlock and msk watchdog timeout

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Hi,

After making world a couple of days ago, my msk(4) became very
unstable.  Under moderate network load, the interface hung and I
received

	kernel: msk0: watchdog timeout (missed Tx interrupts) -- recovering

at least once every several minutes and 

	kernel: msk0: Rx FIFO overrun!

occasionally.

It was so annoying that I took the trouble of binary searching the
kernel version to find the one destabilized my msk(4).

The outcome of the search turned out te be strange.  Instead of
finding a date after which msk(4) became so very unstable, it *seemed*
that the older the kernel version the stabler msk(4) I got, and the
newer the kernel version the easier and more often msk(4) hung.

I managed to pin down that with the kernel as of 2007.06.04.12.00.00,
it seemed not to give me any msk watchdog timeout at all, and that
with the kernel as of 2007.06.05.12.00.00, msk(4) began to hang and
the watchdog began to timeout once in a while.  There may be a latter
commit that made my msk(4) even more unstable, but I am not sure about
this part as it is not easy to measure the level of "unstableness" of
the network.

It seems that the most significant commit between 2007.06.04.12.00.00
and 2007.06.05.12.00.00 was threadlock by jeff_at_.  I don't know why or
how it would affect msk(4), though.  I was using SCHED_SMP on a C2D,
but switched back to SCHED_ULE when I did the search.

I discovered a couple other funny phenomena during the search that may
also suggest this be related to threadlock.  One is that msk(4) seemed
to hang less frequently when the system was busy building world or
kernel.  The other thing is that I seemed to be able to help unhang
the interface by switching the input focus in X Window by move my
mouse cursor to another window.

My result might not be accurate, though, as I only rebuilt the kernel,
not the whole world, when I did the search.

- -- llwang
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