linux-kernel - Re: [PATCHSET 0/4] perf report: Support folded callchain output (v4)

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Date:	Wed, 4 Nov 2015 10:54:33 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Brendan Gregg <brendan.d.gregg@...il.com>
CC:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Kan Liang <kan.liang@...el.com>
Subject: Re: [PATCHSET 0/4] perf report: Support folded callchain output (v4)

Hi Brendan,

On Tue, Nov 03, 2015 at 01:33:43PM -0800, Brendan Gregg wrote:
> On Tue, Nov 3, 2015 at 6:40 AM, Arnaldo Carvalho de Melo
> <arnaldo.melo@...il.com> wrote:
> > Em Tue, Nov 03, 2015 at 09:52:07PM +0900, Namhyung Kim escreveu:
> >> Hello,
> >>
> >> This is what Brendan requested on the perf-users mailing list [1] to
> >> support FlameGraphs [2] more efficiently.  This patchset adds a few
> >> more callchain options to adjust the output for it.
> >>
> >>  * changes in v4)
> >>   - add missing doc update
> >>   - cleanup/fix callchain value print code
> >>   - add Acked-by from Brendan and Jiri
> >
> > Do those Acked-by stand? Things changed, the values moved from the end
> > of the line to the start, etc.
> >
> [...]
> 
> I'd Ack this change as it's a useful addition. It doesn't quite
> address the folded-only output, but it's a step in that direction. I
> think having the value at the start of a line only makes sense for the
> perf report output containing the hist summary lines, for consistency.

Right, thanks!


> 
> Here's how I'd shuffle the output of this patch (ignore word wrap
> issues with this email):
> 
> # ./perf report --stdio -g folded,count,caller -F pid | \
>     awk '/^ / { n = $1 }
>     /^[0-9]/ { split(n,a,":"); print a[2] "-" a[1] ";" $2,$1 }'
> swapper-0;cpu_bringup_and_idle;cpu_startup_entry;default_idle_call;arch_cpu_idle;default_idle;xen_hypercall_sched_op
> 809
> swapper-0;xen_start_kernel;x86_64_start_reservations;start_kernel;rest_init;cpu_startup_entry;default_idle_call;arch_cpu_idle;default_idle;xen_hypercall_sched_op
> 135
> dd-30551;__GI___libc_read;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;urandom_read;extract_entropy_user;extract_buf;check_events;xen_hypercall_xen_version
> 63
> dd-30551;__GI___libc_read;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;urandom_read;extract_entropy_user;extract_buf
> 54
> dd-30551;__GI___libc_read;entry_SYSCALL_64_fastpath;sys_read;vfs_read;__vfs_read;urandom_read;extract_entropy_user;extract_buf;memset_erms
> 3
> dd-30551;xen_irq_enable_direct_end;check_events;xen_hypercall_xen_version 3
> 
> So the output is folded stacks, prefixed by comm-PID. Shuffling the
> summarized output is a lot better than doing a "perf script" dump and
> re-processing call chains. (Note that since I'm using -F, I didn't
> need --no-children;

Nope.  The '-F pid' doesn't affect --children.  It doesn't show the
children overhead column but we still have hist entries for
(synthesized) children..

  $ perf report --no-children | wc -l
  998

  $ perf report --no-children -F pid,dso,sym | wc -l
  998

  $ perf report --children | wc -l
  3229

  $ perf report --children -F pid,dso,sym | wc -l
  3202

So I think you still need to use --no-children (or set report.children
config variable to false) for your script.


> and with "-g count", I didn't need --show-nr-samples.)

Yes, I used -n/--show-nr-samples just to check the number is correct.


> 
> I notice the fields (-F) option already has this precedent:
> 
> - "comm": prints PID:comm
> - "pid": prints PID

It's opposite:  "comm" prints comm, "pid" prints PID:comm. :)


> 
> If these were added to -g, along with a no-hists, then the two types
> of folded-only output could be generated using:
> 
> perf report --stdio -g folded,count,comm,no-hists,caller
> perf report --stdio -g folded,count,pid,no-hists,caller

As I said, using fields like comm, pid requires to have same keys in
--sort option.  So it's basically unreliable to use those specific
field names in the -g option IMHO.  I suggested to use 'info' (yes, it
needs better name) to print all sort keys.


> 
> ... although "no-hists" doesn't hit me as intuitive. How about "-F
> none" to specify zero columns? ie:
> 
> perf report --stdio -g folded,count,comm,caller -F none
> perf report --stdio -g folded,count,pid,caller -F none

Ah, makes sense.  So it'd look like

  $ perf report --stdio -g folded,count,info -F none -s comm
  $ perf report --stdio -g folded,count,info -F none -s pid

The output would be

  809 swapper-0 cpu_bringup_and_idle;cpu_startup_entry;default_idle_call;arch_cpu_idle;default_idle;xen_hypercall_sched_op

Thoughts?

Thanks,
Namhyung
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