Re: Introduce curlwp_bind and curlwp_unbind for psref(9)

[Masao Uebayashi <uebayasi%gmail.com@localhost>]

On Tue, Jun 28, 2016 at 10:08 AM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> On Sat, Jun 25, 2016 at 11:56 AM, matthew green <mrg%eterna.com.au@localhost> wrote:
>>> > Since we already use preempt_disable() to force an lwp to stick to a cpu,
>>> > doesn't that solve the problem?  If need be, we can enforce nonpreemptable
>>> > lwp's don't migrate.
>>
>> why would we want to disable preemption in code that merely wants
>> to run on a particular cpu.
>>
>> i dno't understand why using the side effect of preempt_disable()
>> is better than  explicitly stating what is wanted.
>
> Yes. That's why the API is introduced.

And by introducing such a primitive function, you're doubling the
number of combinations of primitives...

I hope (some of) you surely understand all the implications of those
combinations ... but I'm not.  I'm even not sure if kpreempt_disable()
really prevents LWPs from migrating between CPUs.  It'd be really
helpful if restrictions are expressed by *strict* assertions.

Could you at least put KASSERT((l->l_pflags & LP_BOUND) == 0) in curlwp_bind()?