Hello dearest all.
I have a question regarding tasklets on MIPS. I suspect that there is a bug in generic MIPS kernel, but I'm not sure yet.
Linux kernel has a couple of so called "checkpoints" when the system should check if there are tasklets to run and run them in the following way :
if (softirq_pending(cpu)) do_softirq();
One of these places is at the end of interrupt handler (do_IRQ()), however this is not the only place. I was under impression that this code should be called after system call too. The caveat here is that on MIPS (contrary to other architectures, such as x86) system call is not an interrupt (it's a different exception) and has completely different handler. So in x86 it is sufficient to call
if (softirq_pending(cpu)) do_softirq();
at the end of do_IRQ because do_IRQ handles system call too, but on MIPS it is not. Therefore I believe these lines should be added to the end of sys_syscall function on MIPS.
What do you think ?
P.S. The whole issue started when we noticed that user process making many system calls has very significant impact on device drivers running in tasklet mode and no impact whatsoever on device drivers running in interrupt mode.