Re: [RFC 1/2] softirq: Defer net rx/tx processing to ksoftirqd context

[Mike Galbraith]

On Fri, 2018-01-12 at 09:51 -0800, Linus Torvalds wrote:
> On Fri, Jan 12, 2018 at 9:44 AM, Mike Galbraith <efault@xxxxxx> wrote:
> >
> > Nah, a misunderstanding happened.  RT that still offers full threading
> > creates per-softirq threads per cpu.  The regular trees split ksoftirqd
> > into only two threads per cpu, one processes timer/hrtimer softriqs,
> > the other processes the rest.
> 
> Ok, that sounds like it should work, but it also sounds like it's very
> specific to RT itself.
> 
> For example, the dvb issue was not about the timer softirqs, but about
> the tasklet ones.
> 
> So maybe we wouldn't need to split it for _every_ softirq, but we'd
> need to split it more than just along the timer case.
> 
> And it does sound a bit excessive to have ten fixed threads for every
> CPU. The days when tens of CPU's meant "huge system" are gone. These
> days it can be a phone.

Yeah, it is excessive more often than not.  You get to prioritize, and
segregate, which is nice, but you pay for it.

	-Mike