linux-kernel - Re: [PATCH 3/5] intel_pstate: remove intel

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Message-ID: <1534231.XqQ6Lv6Ybd@aspire.rjw.lan>
Date:   Sat, 17 Jun 2017 03:21:32 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Len Brown <lenb@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PM list <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 3/5] intel_pstate: remove intel_pstate.get()

On Friday, June 16, 2017 09:10:39 PM Len Brown wrote:
> >> >> -             get_avg_frequency(cpu),
> >> >> +             aperfmperf_khz_on_cpu(cpu->cpu),
> >>
> >> Note that I deleted the line above in an updated version of this patch
> >> that I'm ready to send out.
> >>
> >> There were a couple of problems with it.
> >> The first is that it was  ugly that tracing (which occurs only in the
> >> SW governor case)
> >> could shorten the measurement interval as seen by the sysfs interface.
> >>
> >> The second is that this trace point can be called with irqs off,
> >> and smp_call_function_single() will WARN when called with irqs off.
> >>
> >> Srinivas Acked that I simply remove this field from the tracepoint --
> >> as it is redundant to calculate it in the kernel when we are already
> >> exporting the raw values of aperf and mperf.
> >
> > This changes the tracepoint format and I know about a couple of user space
> > scripts that consume these tracepoints though.
> > What would be wrong with leaving it as is?
> 
> I'm fine keeping get_avg_frequency() for the purpose of just this tracepoint
> compatibility, if you think it is useful to do so.
> 
> I removed it because its only function was the (removed) intel_pstate.get()
> and this tracepoint.  And this tracepoint already includes aperf and mperf,
> which can be used to calculate frequency in user-space, if desired.
> Srinivas Acked' that updating his user-space script would be fine --
> dunno if that is sufficient.

Well, we can try to make this change and see if there are any complaints
about it.

But the Srinivas' script is in the tree, so it would be good to update it too
along with the tracepoint.

Thanks,
Rafael