On Wed, Sep 20 2023 at 17:58, Ankur Arora wrote:
> Thomas Gleixner <tglx@xxxxxxxxxxxxx> writes:
>> So no, we don't need yet another knob. We keep them chucking along and
>> if they really want they can adopt to the new world order. :)
>
> Will they chuckle along, or die trying ;)?
Either way is fine :)
> I grepped for "preempt_enable|preempt_disable" for all the archs and
> hexagon and m68k don't seem to do any explicit accounting at all.
> (Though, neither do nios2 and openrisc, and both csky and microblaze
> only do it in the tlbflush path.)
>
> arch/hexagon 0
> arch/m68k 0
...
> arch/s390 91
> arch/mips 115
> arch/x86 146
> arch/powerpc 201
>
> My concern is given that we preempt on timeslice expiration for all
> three preemption models, we could end up preempting at an unsafe
> location.
As I said in my reply to Linus, that count is not really conclusive.
arch/m68k has a count of 0 and supports PREEMPT for the COLDFIRE
sub-architecture and I know for sure that at some point in the past
PREEMPT_RT was supported on COLDFIRE with minimal changes to the
architecture code.
That said, I'm pretty sure that quite some of these
preempt_disable/enable pairs in arch/* are subject to voodoo
programming, but that's a different problem to analyze.
> Still, not the most pressing of problems.
Exactly :)
Thanks,
tglx
