From: Saravana Kannan <skannan@codeaurora.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
Rafael Wysocki <rjw@rjwysocki.net>,
Ingo Molnar <mingo@redhat.com>,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
smuckle.linux@gmail.com, eas-dev@lists.linaro.org
Subject: Re: [Eas-dev] [PATCH V3 2/3] cpufreq: schedutil: Process remote callback for shared policies
Date: Wed, 26 Jul 2017 13:56:10 -0700 [thread overview]
Message-ID: <597901EA.6080702@codeaurora.org> (raw)
In-Reply-To: <20170720122239.licc6yjd7jwipcvk@hirez.programming.kicks-ass.net>
On 07/20/2017 05:22 AM, Peter Zijlstra wrote:
> So the typical implementation of fast switching we're thinking of is the
> CPU writing the DVFS request into a machine register. Now machine
> registers are typically per logical CPU.
Writing to a memory addressable register. AFAIK, ARM has no support for
a machine register for DVFS request. So, even if any ARM licensee wants
to add one, it won't be possible.
Also, even if we have an ARM CPU with a machine register, rejecting a
valid frequency switch just because it happened to come on a different
CPU seem silly (you can have a huge performance hit due to that). A much
better solution is to just make an IPI to the right CPU and execute the
machine register write on the right CPU.
-Saravana
--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
next prev parent reply other threads:[~2017-07-26 20:56 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-13 6:44 [PATCH V3 0/3] sched: cpufreq: Allow remote callbacks Viresh Kumar
2017-07-13 6:44 ` [PATCH V3 1/3] sched: cpufreq: Allow remote cpufreq callbacks Viresh Kumar
2017-07-21 13:03 ` Peter Zijlstra
2017-07-24 11:01 ` Viresh Kumar
2017-07-24 13:47 ` Peter Zijlstra
2017-07-26 6:29 ` Viresh Kumar
2017-07-26 8:12 ` Peter Zijlstra
2017-07-26 17:26 ` Rafael J. Wysocki
2017-07-26 21:00 ` [Eas-dev] " Saravana Kannan
2017-07-27 3:30 ` Viresh Kumar
2017-07-27 19:55 ` Saravana Kannan
2017-07-28 4:33 ` Joel Fernandes (Google)
2017-07-28 6:00 ` Viresh Kumar
2017-07-28 21:05 ` Saravana Kannan
2017-07-31 3:58 ` Viresh Kumar
2017-07-13 6:44 ` [PATCH V3 2/3] cpufreq: schedutil: Process remote callback for shared policies Viresh Kumar
2017-07-14 2:02 ` [Eas-dev] " Saravana Kannan
2017-07-14 5:03 ` Viresh Kumar
2017-07-20 13:58 ` Peter Zijlstra
2017-07-20 12:22 ` Peter Zijlstra
2017-07-20 15:11 ` Sudeep Holla
2017-07-26 20:56 ` Saravana Kannan [this message]
2017-07-13 6:44 ` [PATCH V3 3/3] cpufreq: governor: " Viresh Kumar
2017-07-13 15:17 ` [PATCH V3 0/3] sched: cpufreq: Allow remote callbacks Rafael J. Wysocki
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