Re: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event

[Stephane Eranian]

Hi Jiri,

On Thu, Jun 7, 2018 at 8:45 AM Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>
> On Thu, Jun 07, 2018 at 12:15:12AM +0200, Jiri Olsa wrote:
> > Disable stopping of the idle tick when having live cputime
> > event. When the tick is disabled, the idle counts are out
> > of date until next tick/update and perf cputime PMU provides
> > misleading counts.
>
> I really don't like this. This can totally change performance
> (e.g. less Turbo due to less idle) and performance tools shouldn't
> change the performance profile drastically.
>
You do not want to change the behavior of the kernel just because you
are monitoring.
This may introduce side effects on other events which may not otherwise exist.