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To: David Xu <davidxu@freebsd.org>
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Subject: Re: svn commit: r214409 - head/sys/kern
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On 27 Oct 2010, at 13:56, David Xu wrote:

>> Yay, it's fd_set all over again :-).
>>=20
>> It sounds like we might just need to add a sysctl and a few wrapper =
functions in userspace along the lines of (hand-wave):
>>=20
>> cpuset_t    *cpuset_alloc();
>> void         cpuset_free();
>>=20
>> And perhaps some sort of API that abstracts manipulation of the set =
(or
>> doesn't but allows the user to easily query its bounds).

> Problem is who will use the non-standard interface ? The =
pthread_attr_getaffinity_np pthread_attr_setaffinity_np
> and others are from glibc, which let you specify arbitrary
> cpuset size but kernel only accept one size.  :-)
>=20
> Though it is not POSIX, but some software start to use it, AFAIK,
> Erlang language's VM start to use it for binding its scheduler
> thread to cpu, we have to live with it. We still lack of some =
functions
> to let it compile without modification, one is it wants to know
> cpu topology, and other crappy functions it wants to use is:
> sched_getaffinity, sched_setaffinity, which one guy thought each
> thread is just a process which has a  PID.  :-)
> I don't know how it uses Solaris processor binding interface.

I see two separate problems here:

(1) Providing potentially non-portable APIs that do the right thing, and =
do it well.

(2) Providing definitely portable APIs whose implementation is as robust =
as possible given their flawed semantics. I.e., don't crash on common =
use.

The latter should be implemented in terms of the former.

Robert=