linux-kernel - Re: [PATCH 34/37] perf hists browser: Support flat callchains

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Message-ID: <20151124052708.GB2636@sejong>
Date:	Tue, 24 Nov 2015 14:27:08 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Andi Kleen <andi@...stfloor.org>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>,
	Kan Liang <kan.liang@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH 34/37] perf hists browser: Support flat callchains

On Mon, Nov 23, 2015 at 04:16:48PM +0100, Frederic Weisbecker wrote:
> On Thu, Nov 19, 2015 at 02:53:20PM -0300, Arnaldo Carvalho de Melo wrote:
> > From: Namhyung Kim <namhyung@...nel.org>
> > 
> > The flat callchain mode is to print all chains in a single, simple
> > hierarchy so make it easy to see.
> > 
> > Currently perf report --tui doesn't show flat callchains properly.  With
> > flat callchains, only leaf nodes are added to the final rbtree so it
> > should show entries in parent nodes.  To do that, add parent_val list to
> > struct callchain_node and show them along with the (normal) val list.
> > 
> > For example, consider following callchains with '-g graph'.
> > 
> >   $ perf report -g graph
> >   - 39.93%  swapper  [kernel.vmlinux]  [k] intel_idle
> >        intel_idle
> >        cpuidle_enter_state
> >        cpuidle_enter
> >        call_cpuidle
> >      - cpu_startup_entry
> >           28.63% start_secondary
> >         - 11.30% rest_init
> >              start_kernel
> >              x86_64_start_reservations
> >              x86_64_start_kernel
> > 
> > Before:
> >   $ perf report -g flat
> >   - 39.93%  swapper  [kernel.vmlinux]  [k] intel_idle
> >        28.63% start_secondary
> >      - 11.30% rest_init
> >           start_kernel
> >           x86_64_start_reservations
> >           x86_64_start_kernel
> > 
> > After:
> >   $ perf report -g flat
> >   - 39.93%  swapper  [kernel.vmlinux]  [k] intel_idle
> >      - 28.63% intel_idle
> >           cpuidle_enter_state
> >           cpuidle_enter
> >           call_cpuidle
> >           cpu_startup_entry
> >           start_secondary
> >      - 11.30% intel_idle
> >           cpuidle_enter_state
> >           cpuidle_enter
> >           call_cpuidle
> >           cpu_startup_entry
> >           start_kernel
> >           x86_64_start_reservations
> >           x86_64_start_kernel
> > 
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > Tested-by: Brendan Gregg <brendan.d.gregg@...il.com>
> > Cc: Andi Kleen <andi@...stfloor.org>
> > Cc: David Ahern <dsahern@...il.com>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Jiri Olsa <jolsa@...hat.com>
> > Cc: Kan Liang <kan.liang@...el.com>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Link: http://lkml.kernel.org/r/1447047946-1691-8-git-send-email-namhyung@kernel.org
> > Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> > ---
> 
> [...]
> 
> > +int callchain_node__make_parent_list(struct callchain_node *node)
> > +{
> > +	struct callchain_node *parent = node->parent;
> > +	struct callchain_list *chain, *new;
> > +	LIST_HEAD(head);
> > +
> > +	while (parent) {
> > +		list_for_each_entry_reverse(chain, &parent->val, list) {
> > +			new = malloc(sizeof(*new));
> > +			if (new == NULL)
> > +				goto out;
> > +			*new = *chain;
> > +			new->has_children = false;
> > +			list_add_tail(&new->list, &head);
> > +		}
> > +		parent = parent->parent;
> > +	}
> > +
> > +	list_for_each_entry_safe_reverse(chain, new, &head, list)
> > +		list_move_tail(&chain->list, &node->parent_val);
> > +
> > +	if (!list_empty(&node->parent_val)) {
> > +		chain = list_first_entry(&node->parent_val, struct callchain_list, list);
> > +		chain->has_children = rb_prev(&node->rb_node) || rb_next(&node->rb_node);
> > +
> > +		chain = list_first_entry(&node->val, struct callchain_list, list);
> > +		chain->has_children = false;
> 
> I'm a bit puzzled with this, can't we rewind through the parents on printing or adding
> to the flat rbtree instead of having this parent_val field?

Yes, this code is to simplify things on parent nodes.  Maybe we could
go up to parents and print the callchain list there as you said.

However, problem I think is how to handle 'has_children' information
on parents.  That info controls folding status of each callchain.  As
the info is in the struct callchain_list and flat or folded callchain
mode require the info should be in the top-most entry, I cannot share
entries in parent nodes.

Thus I simply copied callchain lists in parents to leaf nodes.  Yes,
it will consume some memory but can simplify the code.

Thank you for your review anyway!
Namhyung
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