linux-kernel - Re: [PATCH 2/2] x86: implement multiple queues for smp function call IPIs

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Message-ID: <20080801141743.GV23938@one.firstfloor.org>
Date:	Fri, 1 Aug 2008 16:17:43 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86: implement multiple queues for smp function call IPIs

> So ... how about my original suggestion, to add a (default-off) boot 
> option that reduces the queues to 1? I.e. lets have something in place 
> from day 1 on that could be quirk-handler-driven, should the need arise. 
> "apic=simpleipi" or something like that.
> 
> In a year or two, once this all has proven itself fine on a broad range 
> of systems, we'll laugh out loud at being so cautious and can remove the 
> boot option for good ;-)

I agree that adding a boot option to turn it off is a good idea (assuming
it doesn't take too much code to implement) Adding such paranoid boot options early 
has saved my ass a few times in the past.

Only tricky bit is use if () not "modulo variable", because the if ()
will be much faster than a division through an arbitary number.

-Andi
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