linux-kernel - Re: [patch 1/2] x86, x2apic: minimize IPI register writes using cluster groups v4

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Date:	Tue, 3 May 2011 08:31:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [patch 1/2] x86, x2apic: minimize IPI register writes using
 cluster groups v4

* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> On 05/02/2011 07:05 PM, Ingo Molnar wrote:
> ...
> >>
> >>   Ingo, would it be fine to make apic->init() either _before_ this series or 
> >> on top of them (because if I introduce it inside this particular patch it 
> >> would contain some unrelated code snippets such as .init = NULL for all apics 
> >> declaration).
> > 
> > Of course it should be a separate patch - even this patch looks a bit large - 
> > any way to split it up further?
> 
>   Well, for this particular path the only minimum is used, so i fear there is no
> way to split it, probably I could drop some 'cleanup' bits from it and make it
> a separate one. Gimme some time.

Well, first try to do *all* preparatory and cleanup changes that have low 
regression risk.

*Then* keep the most dangerous part to the end of it - so that it's easily 
reverted, should the need arise. Preferably the dangerous part should be much 
smaller than:

 3 files changed, 136 insertions(+), 46 deletions(-)

And no, it is not at all true that there is 'no way' to split the patch up any 
further: you could certainly add the data structures, init methods and such 
support code (which is low regression risk) in a separate patch than the 
changes that modify the existing x2apic_send_IPI_mask_allbutself() function and 
such.

Also, the loop body in the new __x2apic_send_IPI_mask() function could 
certainly be split out into a helper inline, making the code flow clearer.

Thanks,

	Ingo
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