linux-kernel - Re: [PATCH] stack and rcu interaction bug in smp_call_function

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Date:	Sun, 10 Aug 2008 21:34:21 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Ingo Molnar <mingo@...e.hu>, npiggin@...e.de,
	linux-kernel <linux-kernel@...r.kernel.org>,
	suresh.b.siddha@...el.com
Subject: Re: [PATCH] stack and rcu interaction bug in
 smp_call_function_mask()

On Sun, 10 Aug 2008 21:26:18 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Nick Piggin wrote:
> > Nice debugging work.
> >
> > I'd suggest something like the attached (untested) patch as the
> > simple fix for now.
> >
> > I expect the benefits from the less synchronized,
> > multiple-in-flight-data global queue will still outweigh the costs
> > of dynamic allocations. But if worst comes to worst then we just go
> > back to a globally synchronous one-at-a-time implementation, but
> > that would be pretty sad! 
> 
> What if we went the other way and strictly used queue-per-cpu?  It
> means multicast would require multiple enqueueing operations, which
> is a bit heavy, but it does make dequeuing and lifetime management
> very simple...

as long as send-to-all is still one apic operation.. otherwise it gets
*really* expensive....
(just think about waking all cpus up out of their C-states.. one by one
getting the full exit latency sequentially)

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