linux-kernel - Re: [PATCH 08/20] powerpc: Preemptible mmu

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Message-ID: <1283246084.2059.66.camel@laptop>
Date:	Tue, 31 Aug 2010 11:14:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...e.de>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH 08/20] powerpc: Preemptible mmu_gather

On Tue, 2010-08-31 at 16:31 +1000, Benjamin Herrenschmidt wrote:

> Of course, with -rt and the pte lock becoming a mutex, all of your
> changes do become necessary (and I suppose that's where they come from).
>
> Now, those changes won't technically hurt on a non-rt kernel, tho they
> will add a tiny bit of overhead. I'll see if I can measure it.

Indeed, those parts are only strictly needed for -rt, I was hoping the
tiny bit of overhead wouldn't be too bad and we could keep it.

If not I guess we should put those two bits in __switch_to() under
CONFIG_PREEMPT_RT and carry them there for a little while longer.

> > I suppose that's what's causing the similar patch you have in -rt to
> > fail btw. This could be fixed easily by using "current" instead.
> 
> And here's a fix. Using current_thread_info() everywhere is better
> anyways, you are not supposed to touch the local_flags within anything
> but "current" so we may as well make it explicit.
> 
> Feel free to fold that into your -rt patch and this one if you decide
> not to drop that whole part. 

Thanks! And yeah I'd prefer to keep it to reduce Thomas' burden if
possible.


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