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Message-ID: <1410511293.5547.33.camel@marge.simpson.net>
Date: Fri, 12 Sep 2014 10:41:33 +0200
From: Mike Galbraith <umgwanakikbuti@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: perf top -g -U --sort=symbol --children == lalalalala?
On Fri, 2014-09-12 at 16:24 +0900, Namhyung Kim wrote:
> Hi Arnaldo and Mike,
>
> On Thu, 11 Sep 2014 10:43:38 -0300, Arnaldo Carvalho de Melo wrote:
> > Em Thu, Sep 11, 2014 at 02:43:12PM +0200, Mike Galbraith escreveu:
> >> On Thu, 2014-09-11 at 17:09 +0900, Namhyung Kim wrote:
> >> > On Tue, Sep 9, 2014 at 10:37 PM, Arnaldo Carvalho de Melo
> >> > <acme@...stprotocols.net> wrote:
> >> > > Em Tue, Sep 09, 2014 at 01:54:01PM +0200, Mike Galbraith escreveu:
> >> > >> Seems the now default on --children thingy doesn't like -U much.
> >> > >
> >> > > Namhyung, can you please take a look at this?
> >> >
> >> > So what is the problem here?
> >>
> >> Well, if you don't see anything wrong, I guess nothing at all.
> >
> > :-)
> >
> > I think that when we decide that it is so better to change defaults like
> > we did this time, we should be required to add a big fat warning (a
> > --tui popup, use the first lines on --stdio, etc) about why the default
> > was changed and allow quick, easy opt out, restoring previous behaviour
> > after the user, being warned, knows what to expect, tries it, and then
> > is in a better position to decide if keeping the new default is what is
> > desired.
>
> So the problem is that why it turned on --children option by default,
> right? I thought you mentioned there's a problem with -U option and I
> couldn't figure out what it is.
>
>
> >
> >> > >> Samples: 5K of event 'cycles', Event count (approx.): 2268660922
> >> > >> Children Self Symbol
> >> > >> + 46.42% 0.04% [k] system_call_fastpath
> >
> >> I'll just turn it off until I figure out what cool stuff this is telling
> >> me. why that symbol becomes the number one hit, and why total% > 100.
> >
> >> To me, it looks like top smoked it's breakfast, went to lala land ;-)
> >
> > Yeah, its confusing, I'll let Namhyung explain it ;-)
>
> Now I have three persion yell at me for this change. :)
>
> When this change was developping, Ingo said it'd be better if it looks
> like output of sysprof as it's more popular for most (userland?) guys.
> You can see the discussion in the following links:
>
> https://lkml.org/lkml/2013/10/31/97
> https://lkml.org/lkml/2013/11/1/85
>
> The children field is a cumulative total overhead (for its all
> children/callee) so sum of them would be more than 100%. And as Ingo
> requested it sorts the output entries using children overhead so that
> one can easily see higher level view of performance bottle-neck.
I still don't get why my #1 _KERNEL_ (-U) overhead in the below changes
from __schedule() to system_call(). The thing that's consuming the most
cycles remains __schedule(). It doesn't really matter much I 'spose,
turning it off in .perfconfig works fine.
(seems top wants to learn to ignore cpu_startup_entry too [see hmm
below], and maybe grow an option to _not_ ignore idle stuff)
--no-children
- 6.52% [k] __schedule
- __schedule
- 56.95% schedule
99.88% pipe_wait
pipe_read
new_sync_read
vfs_read
sys_read
system_call
__read_nocancel
__libc_start_main
+ 40.63% schedule_preempt_disabled
+ 1.03% __read_nocancel
0.78% pipe_wait
pipe_read
new_sync_read
vfs_read
sys_read
system_call
__read_nocancel
__libc_start_main
+ 0.62% cpu_startup_entry <== hmm
+ 5.13% [k] native_sched_clock
+ 4.80% [k] system_call
+ 4.36% [k] resched_curr
+ 3.59% [k] _raw_spin_lock_irqsave
+ 3.34% [k] __switch_to
--children
+ 68.49% 4.92% [k] system_call
+ 32.75% 0.42% [k] sys_write
+ 31.85% 0.86% [k] vfs_write
+ 30.20% 0.43% [k] sys_read
+ 29.34% 0.74% [k] new_sync_write
+ 29.22% 0.62% [k] vfs_read
+ 27.88% 0.70% [k] new_sync_read
+ 27.65% 1.70% [k] pipe_write
+ 26.62% 2.86% [k] cpu_startup_entry <== hmm
+ 26.23% 2.05% [k] pipe_read
+ 22.38% 0.45% [k] __wake_up_sync_key
- 21.92% 6.61% [k] __schedule
- __schedule
- 62.95% schedule
99.88% pipe_wait
pipe_read
new_sync_read
vfs_read
sys_read
system_call
__read_nocancel
+ 35.27% schedule_preempt_disabled
+ 1.38% __read_nocancel
+ 20.53% 0.81% [k] __wake_up_common
+ 19.72% 0.17% [k] autoremove_wake_function
+ 19.55% 0.09% [k] default_wake_function
+ 19.01% 1.44% [k] try_to_wake_up
+ 18.65% 0.84% [k] pipe_wait
+ 15.07% 1.06% [k] schedule
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