linux-kernel - Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack

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Message-ID: <20160719000801.GS2279@X58A-UD3R>
Date:	Tue, 19 Jul 2016 09:08:01 +0900
From:	Byungchul Park <byungchul.park@....com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>, peterz@...radead.org,
	linux-kernel@...r.kernel.org, walken@...gle.com,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 1/2] x86/dumpstack: Optimize save_stack_trace

On Mon, Jul 18, 2016 at 08:09:10AM -0500, Josh Poimboeuf wrote:
> > > > There are several different users of save_stack_trace() in the kernel, we can't
> > > > be sure that all of them are interested in dropping those guesses.
> > > > 
> > > > So I'd rather advocate in favour of a new seperate helper.
> > > 
> > > So how about we change save_stack_trace() to use print_context_stack()
> > > for CONFIG_FRAME_POINTER=n and print_context_stack_bp() for
> > > CONFIG_FRAME_POINTER=y?  That would preserve the existing behavior, no?
> > 
> > Even if CONFIG_FRAME_POINTER=y, someone may want to guess, doesn't they?
> 
> For CONFIG_FRAME_POINTER=y, the guesses are ignored by
> __save_stack_address() and only the reliable addresses are saved.

Indeed. I was confused.

> We shouldn't change that behavior, unless you actually know of a caller
> who wants the guesses.  And even then the "guess" variation should be
> named accordingly to make it clear that it's not a "reliable" stack
> trace, even though frame pointers are enabled.

My question was caused by being confused. I agree with you.

> 
> -- 
> Josh