Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 8 Nov 2019 10:39:19 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Linux PM <linux-pm@vger.kernel.org>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Doug Smythies <dsmythies@telus.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Giovanni Gherdovich <ggherdovich@suse.cz>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>
Subject: Re: [PATCH v2] cpuidle: Use nanoseconds as the unit of time
Message-ID: <20191108093919.GJ4114@hirez.programming.kicks-ass.net>
References: <10494959.bKODIZ00nm@kreacher>
 <3269796.AzLOQfDnpo@kreacher>
 <CAJZ5v0jM3+qMvO6dx=FmK-xF0q3YKOwBf-yUPXSBfRjxJ59Cpg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAJZ5v0jM3+qMvO6dx=FmK-xF0q3YKOwBf-yUPXSBfRjxJ59Cpg@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Fri, Nov 08, 2019 at 02:44:13AM +0100, Rafael J. Wysocki wrote:
> On Thu, Nov 7, 2019 at 3:25 PM Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> >
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Currently, the cpuidle subsystem uses microseconds as the unit of
> > time which (among other things) causes the idle loop to incur some
> > integer division overhead for no clear benefit.
> >
> > In order to allow cpuidle to measure time in nanoseconds, add two
> > additional fields, exit_latency_ns and target_residency_ns, to
> > represent the exit latency and target residency of an idle state
> > in nanoseconds, respectively, to struct cpuidle_state_usage and
> > initialize them with the help of the corresponding values in
> > microseconds provided by drivers.  In addition to that, change
> > cpuidle_governor_latency_req() to return the idle state exit
> > latency constraint in nanoseconds.
> >
> > With that, meeasure idle state residency (last_residency_ns in
> > struct cpuidle_device and time_ns in struct cpuidle_driver) in
> > nanoseconds and update the cpuidle core and governors accordingly.
> >
> > However, the menu governor still computes typical intervals in
> > microseconds to avoid integer overflows.
> 
> Since this addresses all of the comments received by the RFC version
> that was posted over a month ago and I don't see any more issues with
> it, I'm tempted to simply queue it up for 5.5 unless somebody sees a
> good enough reason why that would be a bad idea.

Nah, have at.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>