linux-kernel - Re: [PATCH 2/2] perf,core: use parent avg sample period as child initial period

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Message-ID: <20170125153301.GQ6500@twins.programming.kicks-ass.net>
Date:   Wed, 25 Jan 2017 16:33:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...el.com
Cc:     linux-kernel@...r.kernel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, eranian@...gle.com,
        ak@...ux.intel.com
Subject: Re: [PATCH 2/2] perf,core: use parent avg sample period as child
 initial period

On Wed, Jan 18, 2017 at 08:21:02AM -0500, kan.liang@...el.com wrote:
> From: Kan Liang <kan.liang@...el.com>
> 
> perf brings additional overhead when monitoring the task which
> frequently generates child task.
> 
> When inheriting a event from parent task to child task, the
> sample_period of original parent event (parent_event->parent) will be
> assigned to child event as its initial period, which is usually the
> default sample_period 1.


Why is that mostly 1? I would expect the parent event's sample_period to
ramp up as well.