Re: [RFC][PATCH v2 08/10] smp,irq_work: Use the new irq_work API

[peterz]

On Wed, Aug 19, 2020 at 03:04:56PM -0700, Linus Torvalds wrote:
> On Wed, Aug 19, 2020 at 12:41 PM <peterz@xxxxxxxxxxxxx> wrote:
> >
> > I'm not sure I get the "expensive irq_work queues" argument, I fully
> > agree with you that adding the atomic op is fairly crap.
> 
> There's an atomic op on the actual runing side too, because of the
> whole IRQ_WORK_PENDING thing.
> 
> So you get that double hit.
> 
> Maybe it doesn't matter. I just remember us being very careful to
> avoid any unnecessary atomics in the smp_call_function area, but
> admittedly I haven't worked on that code for a few years, so ..

Patch #3 trades that atomic for a full barrier. Not a massive win on
x86, but still.