I have a problem that manifests itself with SMP
kernels ( tried both 2.2.5 and 2.2.11 ).
I am working on a device driver that generates
an interrupt when data is available. In my interrupt
handler I call queue_task to place a task in the
tq_scheduler queue because I want the processing
to take place outside the context of an interrupt
handler. With the UP kernel this scheme works
fine, unfortunately with the SMP kernel if there's
no I/O going on, the scheduler does not get run as
frequently as I would wish ( runs at about every
10 ticks which is too slow for me) and hence my processing grinds down to unacceptable levels.
It's funny because I can get this thing to run
faster by moving my mouse around, the faster I
move it the faster the processing :-)
Maybe I need a crank on the side of my box. :-)
Well here's my question:
Can you tickle the scheduler to run immediately
and can you pull this trick from an interrupt
handler?
Things that won't work:
- Calling schedule() from the interrupt handler.
- Starting a new task at system initialization
using the task_queue mechanism that gets run once
and waits on a wait queue loop for a wake_up from
the interrupt handler. It appears that a task queue
task is not allowed to sleep on a wait queue.
(This is assuming that the scheduler will run
if there's something on a wait queue and someone
wakes it up).
- Changing the value of HZ. Not unless you tell
me a way of doing this without recompiling the
kernel.
One possible solution would have been to start a
kernel thread that waits on a wait queue loop.
I guess you don't have kernel threads in Linux
(or do you?) so that's out.
You could also start a user thread that calls
a special ioctl that sleeps on a wait queue that
gets woken by the interrupt handler but that's
a really ugly hack.
Any ideas?
Thanks in advance.
Gokhan Sozmen
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