linux-kernel - Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ tracking

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Date:	Tue, 24 May 2016 01:02:43 +0200 (CEST)
From:	Jiri Kosina <jikos@...nel.org>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	live-patching@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Chris J Arges <chris.j.arges@...onical.com>,
	linuxppc-dev@...ts.ozlabs.org, Jessica Yu <jeyu@...hat.com>,
	Petr Mladek <pmladek@...e.com>, Jiri Slaby <jslaby@...e.cz>,
	Vojtech Pavlik <vojtech@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH v2 05/18] sched: add task flag for preempt IRQ
 tracking

On Fri, 20 May 2016, Andy Lutomirski wrote:

> I think it would be negligible, at least for interrupts, since
> interrupts are already extremely expensive.  But I don't love adding
> assembly code that makes them even slower.  The real thing I dislike
> about this approach is that it's not a normal stack frame, so you need
> code in the unwinder to unwind through it correctly, which makes me
> think that you're not saving much complexity by adding the pushes.

I fail to see what is so special about the stack frame; it's in fact 
pretty normal.

It has added semantic value for "those who know", but the others will 
(pretty much correctly) consider it to be a stackframe from a function 
call, and be done with it.

What am I missing?

Thanks,

-- 
Jiri Kosina
SUSE Labs