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

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Message-Id: <1193688468.9928.30.camel@pasglop>
Date:	Tue, 30 Oct 2007 07:07:48 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, tony@...eyournoodle.com,
	paulus@...ba.org, dino@...ibm.com, tytso@...ibm.com,
	dvhltc@...ibm.com, antonb@...ibm.com, rostedt@...dmis.org
Subject: Re: [PATCH, RFC] hacks to allow -rt to run kernbench on POWER


On Mon, 2007-10-29 at 11:50 -0700, Paul E. McKenney wrote:
> Hello!
> 
> A few random patches that permit POWER to pass kernbench on -rt.
> Many of these have more focus on expediency than care for correctness,
> so might best be thought of as workarounds than as complete solutions.
> There are still issues not addressed by this patch, including:
> 
> o	kmem_cache_alloc() from non-preemptible context during
> 	bootup (xics_startup() building the irq_radix_revmap()).
> 
> o	unmap_vmas() freeing pages with preemption disabled.
> 	Might be able to address this by linking the pages together,
> 	then freeing them en masse after preemption has been re-enabled,
> 	but there is likely a better approach.
> 
> Thoughts?

I see a lot of case where you add preempt_disable/enable around areas
that have the PTE lock held...

So in -rt, spin_lock doesn't disable preempt ? I'm a bit worried...
there are some strong requirements that anything within that lock is not
preempted, so zap_pte_ranges() is the obvious ones but all of them would
need to be addressed.

Ben.


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