Really need some help with RTEMS networking semaphores
gregory.menke at gsfc.nasa.gov
gregory.menke at gsfc.nasa.gov
Wed Oct 18 12:45:49 CDT 2006
Eric Norum writes:
> On Oct 18, 2006, at 11:00 AM, gregory.menke at gsfc.nasa.gov wrote:
> > I've been rewriting the Coldfire fec network driver for a week now to
> > try and make it stable under a significant network load and I'm
> > running
> > into considerable trouble with deadlocks and network semaphore issues.
> > The next 2 days are important, if I can't get the driver stable then I
> > will have to abandon the network stack and try to kludge something up
> > with message queues.
> This is the driver from which BSP?
> The uC5282 driver has been pretty solid here.
We took a copy of the u5282 network.c from the 4.7 CVS for our bsp.
> > I have the network task priority == 1, all other tasks lower. 256k in
> > both the mbuf_bytecount and mbuf_cluster_bytecount.
> > The problems mostly manifest in tcp receives by the RTEMS ftpd, but
> > rapid UDP sends also seem to lock up the stack.
> > The tx task always clears the tx queue; loading packets onto the card
> > till its full and dumping the rest. Rx task receives packets, once an
> > mbuf allocation (done with M_DONTWAIT) fails, all remaining rx packets
> > on the card are dumped. Thus the driver (theoretically) never
> > queues tx
> > buffers and will not stall the card waiting for rx mbufs.
> Having the driver throw away transmit buffers doesn't sound like a
> good idea to me.
I'm trying all options to try and keep the stack on its feet.
> > Is it true that the rx and tx tasks can allocate and free mbuffs as
> > needed when they have the network semaphore, OR must additional
> > semaphore release/obtain invocations be used for each and every mbuf
> > manipulation?
> The rule is that if a task makes calls to any of the BSD network code
> it must ensure that it holds the semaphore. The network receive and
> transmit tasks are started with the semaphore held and call
> rtems_bsdnet_event_receive to wait for an event. This call releases
> the semaphore, waits for an event and then reobtains the semaphore
> before returning. In this way the driver never has to explicitly
> deal with the network semaphore. By way of example, have a look at c/
> src/lib/libbsp/m68k/uC5282/network/network.c -- there is no code that
> manipulates the network semaphore.
The driver tasks only use rtems_bsdnet_event_receive. But for some
reason I'm still getting the "failed to release" message. Is there a
way that can be triggered from m_freem()'ing a mbuf that the driver is
Also, how should the rx task request buffers; is it OK to use M_DONTWAIT
so the rx task can dump the rx queue on an allocation failure?
> > Under what conditions does the stack deadlock and what can drivers
> > do to
> > help prevent it from doing so?
> Running out of mbufs is never a good thing. In the UDP send case you
> might reduce the maximum length of the socket queue.
Does that mean a too-long udp send queue can starve for mbufs & deadlock
> > What is the functional relationship between the mbuf_bytecount and
> > mbuf_cluster_bytecount?
> 'regular' (small) mbufs are allocated from the pool sized by
> mbuf_bytecount. mbuf clusters (2k each) are allocated from the pool
> sized by mbuf_cluster_bytecount.
> > What should their relative sizings be?
> Depends on your application. Which type are you running out of?
> For my EPICS applications here I've got:
> 180*1024, /* MBUF space */
> 350*1024, /* MBUF cluster space */
How do I tell which I'm running out of?
I've tried everything from 64k & 128k up to 256k & 256k, some sort of
problems in all cases. Could you give examples of how mbuf buffer
sizings relates to types of application?
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