linux-kernel - Re: [PATCH, RFC] improved hacks to allow -rt to run kernbench on POWER

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Message-Id: <1194947026.18185.95.camel@pasglop>
Date:	Tue, 13 Nov 2007 20:43:46 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	paulmck@...ux.vnet.ibm.com, Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, tony@...eyournoodle.com,
	paulus@...ba.org, dino@...ibm.com, tytso@...ibm.com,
	dvhltc@...ibm.com, niv@...ibm.com, antonb@...ibm.com,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH, RFC] improved hacks to allow -rt to run kernbench on
	POWER


On Tue, 2007-11-13 at 10:10 +0100, Peter Zijlstra wrote:
> 
> Correct, -rt can't allocate -anything- when preemption if off. That is
> the cost for having the allocators itself preemptable.
> 
> Even radix_tree_preload() will not work as its functionality was based
> on preempt disable to limit access to a global (per cpu) object
> reserve.
> But maybe something similar could be done with a local reserve by
> using
> struct radix_tree_context to pass it along.
> 
> I'll see if I can come up with anything like that, that is, if that
> would suffice?

For that specific problem, as long as the radix tree can be made to work
while non-preemptible, I'm fine :-)

I'm still worried by other cases where things expect GFP_ATOMIC to work
at any time.

Ben.


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