Hi Paolo,
If you have a multicpus machine and can reserve CPUs to real time only,
than the picture will change a lot. No Linux activity on them, just your
real time programs and irq handlers, likely stuck and fully cached to
those CPUs.
This is the solution you'll see native in Linux soon. With true lowcost
multicpus on a single chip massively available within a short time at
the kids' game and mama's word processors store it will change the whole
picture.
Actually this is kind of available right now with vanilla 2.6 kernel.
I'm talking about CPU reservation. Here is an example.
Let's say we have dual CPU box and we want to dedicate CPU 1 to
our application:
- Configure the kernel with following boot options:
isolcpus=1 acpi_irq_nobalance noirqbalance
This excludes CPU 1 from the scheduler balancing logic. And disables
ACPI and SW irq balancing.
Make sure that you don't run user-space IRQ balancer.
- Redirect all interrupts to CPU 0
for i in /proc/irq/*; do
echo 1 > $i/smp_affinity;
done
- Your app call now migrate to CPU 1
int cpu = 1;
uint32_t mask = (1 << cpu);
sched_setaffinity(0, sizeof(mask), (cpu_set_t *) &mask);
That's it. CPU 1 is yours. There will be almost zero activity on it, besides
your task of course.
Max
