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

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Date:   Fri, 2 Mar 2018 11:18:10 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Du, Changbin" <changbin.du@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        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 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.