linux-kernel - Re: [PATCH v2] tracing/power: Polish the tracepoints cpu_idle and cpu

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Date:   Fri, 2 Mar 2018 18:15:14 +0800
From:   "Du, Changbin" <changbin.du@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Du, Changbin" <changbin.du@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tracing/power: Polish the tracepoints cpu_idle and
 cpu_frequency

On Fri, Mar 02, 2018 at 11:18:10AM +0100, Rafael J. Wysocki wrote:
> On Fri, Mar 2, 2018 at 10:41 AM, Du, Changbin <changbin.du@...el.com> wrote:
> >> >> That rather isn't the case if negative values are ever passed to the
> >> >> tracepoint, right?
> >> >>
> >> > yes.
> >> >> Which seems to be the reason why you want to make this change, isn't it?
> >> >>
> >> > yes, to improve readability.
> >> >
> >> >> So maybe fix the code using the tracepoint(s) to avoid passing
> >> >> negative values to it(them)?
> >> > For cpu_idle event, [0, CPUIDLE_STATE_MAX) are used to index the idle state arrary,
> >> > so I think a appropriate value for PWR_EVENT_EXIT is -1 (defined in include/trace/events/power.h).
> >> > Or do you have a better idea? Thanks!
> >>
> >> Sorry, I'm not sure what you mean.
> >>
> >> I'm saying that the code using the CPU PM tracepoints is not expected
> >> to pass -1 as the CPU number to them.  IOW, neither -1 nor its UL
> >> representation should ever appear in the output of these tracepoints.
> >> If that happens, it is a problem with the code using the tracepoints
> >> which needs to be fixed.  Users should not see any of these values.
> >
> > This patch only changed 'state' field but cpuid. For cpu_idle event, 'state' is
> > singned value, but for cpu_frequency it is unsinged.
> > The cpuid is always unsinged value. So no one passes -1 as CPU number.
> 
> You are right, 'state' not 'cpuid', sorry.
> 
> Negative 'state' should not be passed to these tracepoints too, though.

The current situtation is that 'state' can be negative for event cpu_idle :(. This
is why I made this change.

-- 
Thanks,
Changbin Du