On Tue, Dec 01, 2020 at 11:45:25AM -0800, Linus Torvalds wrote:
> On Mon, Nov 30, 2020 at 11:56 PM Peter Zijlstra <pet...@infradead.org> wrote:
> >
> > So even if an architecture needs to enable interrupts on idle, we need
> > it disabled again when coming out. So we might as well have the arch
> > idle routine then be: STI; HLT; CLI; because then architectures than can
> > idle with interrupts disabled can avoid mucking about with the interrupt
> > state entirely.
>
> But that's not what the code is doing.
>
> Go look at it.
>
> It does sti;hlt;cli;pushf;cli;sti.
>
> All for no good reason - because the code is structured so that even
> if all the tracking and lockdep is disabled, the pointless "let's
> protect the tracking from interrupts" is still there.
>
> See what I am complaining about?
Absolutely.
default_idle()
arch_cpu_idle()
sti; hlt;
cli;
rcu_idle_exit()
pushf;
cli;
rcu_eqs_exit(false);
popf;
sti;
is what it currently looks like, and that's completely insane, no
argument.
What I would like to end up with is:
default_idle()
arch_cpu_idle()
sti; hlt; cli
rcu_idle_exit()
rcu_eqs_exit(false);
sti;
Which would allow architectures that can idle with IRQs disabled to do
so. But that needs a little more work:
- make arch_cpu_idle() IRQ invariant (we enter and exit with IRQs off)
- make cpuidle drivers do similar
- audit all rcu_idle_exit() callers and remove save/restore
