On Wed, 2011-12-28 at 16:14 +0100, Bjarke Istrup Pedersen wrote:

2011/12/28 Ben Hutchings [off-list ref]:

quoted

On Wed, 2011-12-28 at 12:28 +0000, Bjarke Istrup Pedersen wrote:

quoted

Working around problem causing high CPU load and hanging system when
there is alot of network trafic.

It is kind of an ugly way to work around it, but it allows the Soekris
net5501 to have trafic between two of it's NICs without hanging so much
that the watchdog kicks in and does a hard reboot of the system.

There is more info on the problem here:
http://http://lists.soekris.com/pipermail/soekris-tech/2010-October/016889.html

Tested with positive results on two Soekris net5501-70 boxes.

This is completely wrong.  In a UP configuration the extra spinlock
calls have no effect (except perhaps a small delay).  In an SMP
configuration they will cause rhine_tx() to deadlock when it also tries
to acquire the spinlock.

Ben.

Okay, the Soekris net5501-70 boxes are single-core, and I haven't got
any SMP boxes with that nic.
Is there a better solution for the problem then, to avoid it hanging
the box on a non-smp machine with a slow (500mhz) cpu?

If the system actually hangs then I assume there is some bug in the
driver.  I would guess the actual problem is that the interrupt and NAPI
handlers are running constantly so that user processes never run (which
I think counts as soft lockup).

If the hardware supports it, interrupt moderation may help a little by
slightly reducing the per-packet processing cost, but it isn't a full
solution.  Or you can use a real-time kernel, which schedules interrupt
and NAPI handlers as tasks, and adjust priorities so that user processes
can still run.  But that brings its own problems (including generally
lower throughput).

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.