Michael,
I am not sure what you mean by adding code in interrupt_end to take the
lock. The locking mechanism is present for SMP target, no change required:
externC void
interrupt_end(
cyg_uint32 isr_ret,
Cyg_Interrupt *intr,
HAL_SavedRegisters *regs
)
{
// CYG_REPORT_FUNCTION();
#ifdef CYGPKG_KERNEL_SMP_SUPPORT
Cyg_Scheduler::lock();
#endif
The macro for incrementing the lock in SMP looks at the current owner of
the lock and spin when required.
I found the kernel instrumentation option very useful for debugging
deadlocks. I was using CodeConfidence plugin in Eclipse to analyze the
trace which makes it pretty efficient debugging.
Christophe
On 3/4/2014 4:58 PM, Michael Jones wrote:
Christophe,
When I first got SMP to work I added some code in interrupt_end to take the
lock, but I moved it back to Vectors.S because I was trying to reduce changes
to the kernel. Functionally, the only difference is getting the lock before the
ISR is executed or not.
My bigger concern is how the lock is taken. When I increase the lock count, the
core doing so (core 0) may not be the holder of the lock, which leads to
assertions. And if it spins while taking the lock, it deadlocks. I have not
traced down the deadlock, but I think the problem is in the scheduler, where
some secondary CPU is waiting.
My current solution is to use a trylock in Vectors.S and living with the fact
that when it fails, it will take another real time clock interrupt to try
again. So interrupt_end is not guaranteed to called on each interrupt. This
keeps things simple. All interrupts go to core 0 except inter cpu interrupts.
Some latency is added because taking the lock is not guaranteed.
Other ways to handle this is to send interrupts to all cores, use inter core
interrupts, etc, in an effort to guarantee a lock is incremented by the core
that holds the lock.
I was not able to figure our how i386 handled this. Does anyone know how the
i386 SMP incremented the lock if the core that got the interrupt did not hold
the lock?
Mike
On Mar 4, 2014, at 8:37 AM, christophe <[email protected]> wrote:
Hi Michael,
I might remember wrong but I think in case of SMP target, the lock is not taken
in Vector.S but directly after entering interrupt_end. Of course this is
spinlock based so it might delay posting/scheduling of the DSR.
Christophe
On 3/2/2014 9:19 PM, Michael Jones wrote:
Jurgen,
I think I fully understand how the scheduler locking works during interrupt
now. Vectors.S takes the lock, and interrupt_end clears it. However, the normal
technique of incrementing the lock count does not work with SMP. The problem is
that another CPU may have the lock. Incrementing anyway leads to assertions.
Attempting to take the lock with the spinlock can lead to deadlocks or an
unresponsive network application.
So I changed things so that in Vectors.S, during an interrupt, an attempt at
locking is made. This means trying to take a spinlock that might fail. If the
lock is taken, interrupt_end is called. If the lock fails, interrupt_end is not
called.
This means that a DSR may not be posted on that interrupt. This can cause some
latency based on the real time clock interrupt rate, or time until a thread
switch. However, it is stable and assertion free. Also, a HAL could implement a
timeout on the try spinlock which might reduce latency.
To support the try and testing if the lock was taken, I had to add some
functions to the kernel. The following wiki page has been updated to reflect
the kernel changes.
https://sourceforge.net/p/ecosfreescale/wiki/SMP%20Kernel/
Anyone with SMP knowledge might want to take a look. There may be better
solutions to some of these problems. But at least for now, the IMX6 SMP HAL
seems stable and I can run IO intensive Lua scripts over telnet reliably, even
when the client aborts.
The client abort means telnet has to kill a thread. This was quite a challenge.
Telnet is creating a separate heap for Lua so it can kill the thread and
reclaim memory. The remaining problem is closing file handles. I still get some
assertions when a handle is sometimes killed by a thread that does not own it.
I don't think that can be solved without adding some new functions dedicated to
clean up of file handles by an outside thread.
Mike
On Feb 26, 2014, at 11:40 PM, Lambrecht Jürgen <[email protected]> wrote:
As far as I know the scheduler is started after cyg_user_start(), used by your
application to initialize everything. Do you use cyg_user_start?
Verzonden vanaf Samsung Mobile
-------- Oorspronkelijk bericht --------
Van: Michael Jones <[email protected]>
Datum:
Aan: ecos discuss <[email protected]>
Onderwerp: [ECOS] Scheduler startup question
I have a question about proper scheduler locking startup behavior.
The context is I am cleaning up my iMX6 HAL and attempting to make things work
without a couple of kernel hacks I added to make it work.
The question has to do with sched_lock. By default this has a value of 1, so
during startup the scheduler is locked.
When there is an interrupt, sched_lock is incremented in Vectors.S, and
decremented in interrupt_end.
However, I am getting an assert in sync.h which is part of the BSD stack. The
assert is because it expects the lock to be zero.
The question is, during the startup process, how does the lock get set to zero
after initialization? Is it supposed to stay 1 while hardware is initialized
and through all the constructors, etc? Is it cleared by the scheduler somehow?
Is the HAL supposed to zero it at some point during startup?
My HAL is part of the ARM hal, so if this is device specific, it is the ARM HAL
I am working with.
Mike
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
--
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
