From: "Kasagar, Srinidhi" <srinidhi.kasagar@intel.com>
To: Len Brown <lenb@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
"Brown, Len" <len.brown@intel.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Linux PM list <linux-pm@vger.kernel.org>,
vishwesh.m.rudramuni@intel.com, srinidhi.kasagar@intel.com
Subject: Re: [PATCH v7] cpufreq: Add SFI based cpufreq driver support
Date: Thu, 18 Dec 2014 12:14:14 +0530 [thread overview]
Message-ID: <20141218064414.GA18689@intel-desktop> (raw)
In-Reply-To: <CAJvTdKn71M8edzdereUnDTESxJTpgdLXZjFAULO=aQTA0wnpdA@mail.gmail.com>
On Wed, Dec 17, 2014 at 05:12:43PM -0500, Len Brown wrote:
> >> policy->cpuinfo.transition_latency = CPUFREQ_ETERNAL;
> >
> > But we know the transition latency of this system. Why should we
> > claim it as "unknown"? The sfi_freq_table_entry has latency
> > field - does it not make irrelevant then?
>
> I wrote the SFI spec.
> If I did it again, I would not include the latency field in the FREQ table,
> because Linux does not need it.
>
> >> ondemand will compare this to TRANSITION_LATENCY_LIMIT (10 * 1000 * 1000)
> >> and since -1 is less than 10,000,000; it will be happy.
> >>
> >> > + for (i = 0; i < num_freq_table_entries; i++) {
> >> > + /* detect transition latency */
> >> > + if ((sfi_cpufreq_array[i].latency * 1000) >
> >> > + policy->cpuinfo.transition_latency)
> >> > + policy->cpuinfo.transition_latency =
> >> > + sfi_cpufreq_array[i].latency * 1000;
> >>
> >> delete above 5 lines. every SFI system will have latency
> >> plenty lower than that required by ondemand governor.
>
> There is effectively no customer for the information being provided,
> as there are only two possible outcomes:
>
> 1. The largest value in the table is < 10ms, and ondemand loads
> 2. The largest value in the table is > 10ms and ondemand fails to load.
> #1 is how it should always work on all known SFI platforms.
> #2 is a firmware bug.
>
> Well, we can do #1 with 1 line, and at the same time eliminate
> exposure to firmware bugs in #2.
Ok, as we know the latency of this system (as 100 us), I will hardcode this
with 1 line and remove the rest of detection stuff..
Srinidhi
prev parent reply other threads:[~2014-12-18 6:42 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-11 8:14 [PATCH v7] cpufreq: Add SFI based cpufreq driver support Srinidhi Kasagar
2014-12-11 8:22 ` Viresh Kumar
2014-12-11 9:13 ` Kasagar, Srinidhi
2014-12-16 8:15 ` Len Brown
2014-12-16 10:24 ` Kasagar, Srinidhi
2014-12-17 22:12 ` Len Brown
2014-12-18 6:44 ` Kasagar, Srinidhi [this message]
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