Re: [PATCH 4/8] x86: add support for remotely triggering the block softirq

Ingo Molnar
2008-02-07T10:38:50Z

* Jens Axboe <jens.axboe@oracle.com> wrote:

> > pick up the threaded softirq patches from -rt, those move all
> > softirqs processing into kernel threads. I'd suggest to extend those
> > via wakeup-from-remote functionality - it fits the construct quite
> > naturally. You should also be able to directly observe any
> > performance impact of threaded softirq handlers. (and if you find
> > any, let me know so that we can make it faster :-)
>
> I was just considering that, since I knew -rt moved the softirqs into
> threads. I'll look into it, but may not post anything until after my
> vacation.

we should more seriously investigate kernel thread scalability for
another reason as well: besides -rt, any generic async IO facility we
pick up will likely heavily rely on them. Kernel thread scheduling is
quite a bit lighter than user task scheduling [no TLB flushes, etc.] -
and if it is still not good enough we could probably accelerate them
some more. (and everyone will benefit) irq-context softirqs on the other
hand are quite rigid and bring in many atomicity assumptions so they are
not as natural to program for.

Ingo