linux-kernel - Re: [PATCH 3/6] x86,64: Simplify save

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Date:	Mon, 4 Jul 2011 14:57:45 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jan Beulich <JBeulich@...ell.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 3/6] x86,64: Simplify save_regs()

On Mon, Jul 04, 2011 at 08:20:51AM +0100, Jan Beulich wrote:
> >>> On 02.07.11 at 18:29, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > The save_regs function that saves the regs on low level
> > irq entry is complicated because of the fact it changes
> > its stack in the middle and also because it manipulates
> > data allocated in the caller frame and accesses there
> > are directly calculated from callee rsp value with the
> > return address in the middle of the way.
> > 
> > This complicates the static stack offsets calculation and
> > require more dynamic ones. It also needs a save/restore
> > of the function's return address.
> > 
> > To simplify and optimize this, turn save_regs() into a
> > macro.
> 
> So this got pulled out into a function a couple of releases ago,
> and now it's being converted back? Wasn't the original patch's
> intention to reduce the amount of duplication of generated
> code?

Right. I didn't know there was a conversion a while ago for
this save_regs() from a macro to a func in order to remove
code duplication.

I really did not think about code duplication, considering
it's better to optimize the irq entry path.

What do you guys think? We can still revert the whole patchset.
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