Re: Introduce curlwp_bind and curlwp_unbind for psref(9)

[Matt Thomas <matt%3am-software.com@localhost>]

> On Jun 13, 2016, at 5:53 PM, Ryota Ozaki <ozaki-r%netbsd.org@localhost> wrote:
> 
> On Mon, Jun 13, 2016 at 11:21 PM, Taylor R Campbell
> <campbell+netbsd-tech-kern%mumble.net@localhost> wrote:
>>   Date: Mon, 13 Jun 2016 14:00:16 +0200
>>   From: Joerg Sonnenberger <joerg%bec.de@localhost>
>> 
>>   On Mon, Jun 13, 2016 at 07:36:31PM +0900, Ryota Ozaki wrote:
>>> Currently we do it by open-coding in each place,
>>> but we should provide some API to simplify codes.
>>> riastradh@ suggested curlwp_bind and curlwp_unbind
>>> some time ago (*1) and this patch (*2) just follows
>>> the idea.
>> 
>>   The primary question for me is whether nesting should be allowed or not.
>>   That would mean a reference count behind the flag.
>> 
>> This `reference count' gets stored on the stack.  The caller does:
>> 
>>        int bound = curlwp_bind();
>> 
>>        ... psref_wotsit ...
>> 
>>        curlwp_unbind(bound);
>> 
>> If it was already bound, bound = 1 and curlwp_unbind does nothing; if
>> it was not already bound, bound = 0 and curlwp_unbind unbinds it.
>> 
>> Perhaps the name should be `curlwp_bound_restore' or something else to
>> emphasize this, but I haven't come up with one that I like better on
>> aesthetic grounds.
> 
> - curlwp_bind and curlwp_unbind
> - curlwp_bound_set and curlwp_bound_restore
> - curlwp_bound and curlwp_boundx
> 
> Any other ideas? :)

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.