linux-kernel - Re: [patch 2/2] cpusets: add interleave_over

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Message-Id: <20071027135952.2e8fb323.pj@sgi.com>
Date:	Sat, 27 Oct 2007 13:59:52 -0700
From:	Paul Jackson <pj@....com>
To:	Christoph Lameter <clameter@....com>
Cc:	rientjes@...gle.com, Lee.Schermerhorn@...com,
	akpm@...ux-foundation.org, ak@...e.de, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/2] cpusets: add interleave_over_allowed option

> > You have chosen (1) above, which keeps Choice A as the default.
> 
> There can be different defaults for the user space API via libnuma that 
> are indepdent from the kernel API which needs to remain stable. The kernel 
> API can be extended but not changed.

Yes - the user level code can have different defaults too.

I was discussing what should be the default kernel API.

> None of those [alternatives] sound appealing.  Multiple processes may run
> in one cpuset.

Well, that would justify keeping this choice per-task.  I tend to
agree with that.

But that doesn't justify having to specify it on each system call.

In another reply David recommends against supporting Choice A at all.
I'm inclined to agree with him.  I'll reply there, with more thoughts.

But if we did support Choice A, as a backwards compatible alternative
to Choice B, I'd suggest a per-task mode, not per-system call mode.
This would reduce the impact on the API of the ugly, unobvious, modal
flag needed to select the optional, non kernel default, Choice B
semantics.

I still have low confidence that you (Christoph) and I have the same
understanding of what these Choice A and B are.  Hopefully you can
address that, perhaps by briefly describing these choices in your words.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.925.600.0401
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