linux-kernel - Re: [PATCH]: exec: avoid propagating PF_NO

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Date:	Thu, 28 Nov 2013 15:47:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tejun Heo <htejun@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, zhang.yi20@....com.cn,
	lkml <linux-kernel@...r.kernel.org>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH]: exec: avoid propagating PF_NO_SETAFFINITY into
 userspace child

On Thu, Nov 28, 2013 at 09:38:48AM -0500, Tejun Heo wrote:
> Hey, Peter.
> 
> On Thu, Nov 28, 2013 at 03:31:45PM +0100, Peter Zijlstra wrote:
> > But the WQ_UNBOUND thingies should be just that and should thus not have
> > the NO_SETAFFINITY flag set because there is no valid reason to have it
> > set.
> > 
> > Regardless of whether the threads are shared between unbound workqueues
> > or not.
> 
> Hah?  No, we do not want to allow userland to be able to set
> affinities on any workqueue workers, period.  That's just inviting
> people to do weirdest things and then reporting things like "crypt
> jobs on some of our 500 machines end up stuck on a single cpu once in
> a while" which will eventually be tracked down to some weird shell
> script setting affinity on workers doing something else.
> 
> We really want to insulate workers and pool operation from userland.
> e.g. unbound workqueues now default to per-NUMA affinity unless
> explicitly told not to, which leads to better overall behavior for
> most workloads.  We do wanna keep those details from userland so that
> they can be improved in the future too.

Bah, windows mentality of we know better.

If they do stupid they get stupid; the only thing we should be concerned
about is correctness, they shouldn't be able to crash the system.
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