linux-kernel - Re: [PATCH v3 02/15] x86/dumpstack: Add save_stack_trace()

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Message-ID: <20160913132055.3og4jxc4npqa6cfa@treble>
Date:   Tue, 13 Sep 2016 08:20:55 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Byungchul Park <byungchul.park@....com>
Cc:     peterz@...radead.org, mingo@...nel.org, tglx@...utronix.de,
        walken@...gle.com, boqun.feng@...il.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com
Subject: Re: [PATCH v3 02/15] x86/dumpstack: Add save_stack_trace()_fast()

On Tue, Sep 13, 2016 at 06:45:01PM +0900, Byungchul Park wrote:
> In non-oops case, it's usually not necessary to check all words of stack
> area to extract backtrace. Instead, we can achieve it by tracking frame
> pointer. So made it possible to save stack trace lightly in normal case.
> 
> I measured its ovehead and printed its difference of sched_clock() with
> my QEMU x86 machine. The latency was improved over 80% when
> trace->max_entries = 5.

Again this code will (probably) be obsolete soon.  And another quote
from my previous review:

  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?

-- 
Josh