getaffinity/setaffinity and cpu sets.

[Ceri Davies]

On Thu, Feb 21, 2008 at 01:39:42PM -1000, Jeff Roberson wrote:
> 
> On Thu, 21 Feb 2008, Ceri Davies wrote:
> 
>> On Thu, Feb 21, 2008 at 09:27:41AM +0000, Robert Watson wrote:
>> 
>>> - You don't mention what happens if a process's cpu set changes to preclude a
>>>   CPU the process has a thread with affinity for.  Online, you suggested
>>>   SIGKILL, and I thought maybe a new SIGCPUGONE with a default SIGKILL action
>>>   might be a friendlier model.  We should see what Solaris and others do here
>>>   though.  I like the idea that the affinity is a guarantee in userspace
>>>   because it means that you can rely on it; I'm OK with the idea that your
>>>   thread always runs on the CPUs you have affinity for unless in the
>>>   SIGCPUGONE handler :-).
>> 
>> If a processor set disappears from under a process on Solaris, the
>> process gets moved to the "default" set (or, in other words, they aren't
>> in a set any more).
> 
> Yes, that's ok, but what if the process has requested a specific cpu that 
> it's now no longer allowed to access?  The sets are seperate from the 
> thread's specific requested binding.  If the thread binds to a specific 
> processor within the set and the set disappears what should we do?  What if 
> that process was relying on the binding to access cpu specific features 
> such as tsc?  Allowing it to migrate could then break the code.

OK, I was talking about processor sets; in Solaris, binding to a set
(pset_bind()) and binding to a specific processor (processor_bind()) are
different operations.

A processor that has LWPs bound to it specifically (with processor_bind())
may not be taken offline or marked as spare, unless the operation is forced,
whereupon forcing removes the binding.  Since this is an administrative
choice, it's acceptable.

Ceri
-- 
That must be wonderful!  I don't understand it at all.
                                                  -- Moliere
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