linux-kernel - Re: [RFC GIT PULL] softirq: Consolidation and stack overrun fix

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Message-ID: <20130924082128.GJ9326@twins.programming.kicks-ass.net>
Date:	Tue, 24 Sep 2013 10:21:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@....ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	James Hogan <james.hogan@...tec.com>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Helge Deller <deller@....de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>
Subject: Re: [RFC GIT PULL] softirq: Consolidation and stack overrun fix

On Tue, Sep 24, 2013 at 06:16:53PM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2013-09-24 at 10:04 +0200, Peter Zijlstra wrote:
> > On Tue, Sep 24, 2013 at 11:52:07AM +1000, Benjamin Herrenschmidt wrote:
> > > So if that holds, we have a solid way to do per-cpu. On one side, I tend
> > > to think that r13 being task/thread/thread_info is probably a better
> > > overall choice, I'm worried that going in a different direction than x86
> > > means generic code will get "tuned" to use per-cpu for performance
> > > critical stuff rather than task/thread/thread_info in inflexible ways.
> > 
> > The plus side of per-cpu over per-task is that one typically has a lot
> > less cpus than tasks. Also, its far easier/cheaper to iterate cpus than
> > it is to iterate tasks.
> 
> I don't see how that relates to the above though...

It was a comment on the increase of per-cpu usage in generic code.
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