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Message-ID: <20151021192350.GC32514@kernel.org> Date: Wed, 21 Oct 2015 16:23:50 -0300 From: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> To: Brendan Gregg <brendan.d.gregg@...il.com> Cc: Chandler Carruth <chandlerc@...il.com>, Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Adrian Hunter <adrian.hunter@...el.com>, Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>, Stephane Eranian <eranian@...gle.com>, Wang Nan <wangnan0@...wei.com> Subject: Re: [PATCH 13/16] perf callchain: Switch default to 'graph,0.5,caller' Em Wed, Oct 21, 2015 at 11:28:54AM -0700, Brendan Gregg escreveu: > On Tue, Oct 20, 2015 at 7:21 PM, Chandler Carruth <chandlerc@...il.com> wrote: > > Since Arnaldo asked, I thought I should actually try to respond specifically > > to the question of why I favor the 'caller' view as the default. > > > > On Tue, Oct 20, 2015 at 3:06 AM Arnaldo Carvalho de Melo > > <arnaldo.melo@...il.com> wrote: > >> > >> > IMHO changing that order is not a good idea. Unless many users > >> > complained > >> > about it. > >> > >> Perhaps there are not that many users of callchains because the default > >> is not what they're used to see? > >> > >> Motivation for the change came from a video from Chandler, that > >> resurfaced the callchain default issue, Chandler? > > > > > > So, first and foremost, thanks for fixing some of my gripes about the > > usability of the perf tool, I'm super excited about the changes you're > > making, even if this one isn't among them. > > > > I think the default of caller vs. callee is probably the hardest judgement > > call to make about the right defaults. I can see it going both ways. > > > > When profiling my *system*, or a diverse group of programs or tasks, I often > > find callee useful. Were I a kernel developer, I suspect callee would be > > *dramatically* more common than caller. > > > > For me, what makes the caller view much more frequently desired is that I'm > > usually profiling a fairly isolated application, or benchmark for an > > isolated library. While I always start off with some more system-level > > performance problem, I rarely need a detailed profile to get a reasonable > > idea of what subsystem to stare at, and then I spend days looking at a > > relatively isolated reproduction. > > > > Anyways, for profiling user-land applications, I suspect from my > > conversations with users that "caller" is the more common expectation. > [...] > > I would have said callee is the more common expectation, certainly for > system profilers. I quickly checked various tools to see what their > defaults are: > > callee: > > gdb > lldb > pstack > jstack > perf > stap > ktap > dtrace > kernel oops message > jvm crash > node.js/v8 crash > > caller: > > python traceback sysprof -> http://sysprof.com/screen-shot-4.png > > Python was the only one I knew off-hand that is caller by default (and > it includes the text "most recent call last", suggesting the > developers thought it was necessary to point out that it was > different). Do you know what tools/profilers/debuggers these users are > using? > > I really think people will be surprised if by default perf prints > stacks differently to gdb, lldb, oops messages, etc, etc. That may be > true for a specific developer community (eg, Python), but not for > system profilers. > > Brendan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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