From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Stephen Warren <swarren@wwwdotorg.org>
Cc: Doug Anderson <dianders@chromium.org>,
Russell King - ARM Linux <linux@arm.linux.org.uk>,
Viresh Kumar <viresh.kumar@linaro.org>,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Will Deacon <will.deacon@arm.com>,
John Stultz <john.stultz@linaro.org>,
David Riley <davidriley@chromium.org>,
"olof@lixom.net" <olof@lixom.net>,
Sonny Rao <sonnyrao@chromium.org>,
Santosh Shilimkar <santosh.shilimkar@ti.com>,
Shawn Guo <shawn.guo@linaro.org>,
Stephen Boyd <sboyd@codeaurora.org>,
Marc Zyngier <marc.zyngier@arm.com>,
Stephen Warren <swarren@nvidia.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems#
Date: Tue, 13 May 2014 19:29:52 -0400 (EDT) [thread overview]
Message-ID: <alpine.LFD.2.11.1405131922580.980@knanqh.ubzr> (raw)
In-Reply-To: <alpine.LFD.2.11.1405131908260.980@knanqh.ubzr>
On Tue, 13 May 2014, Nicolas Pitre wrote:
> On Tue, 13 May 2014, Stephen Warren wrote:
>
> > On 05/13/2014 03:50 PM, Doug Anderson wrote:
> > ...
> > > ...but then I found the true problem shows up when we transition
> > > between very low frequencies on exynos, like between 200MHz and
> > > 300MHz. While transitioning between frequencies the system
> > > temporarily bumps over to the "switcher" PLL running at 800MHz while
> > > waiting for the main PLL to stabilize. No CPUFREQ notification is
> > > sent for that. That means there's a period of time when we're running
> > > at 800MHz but loops_per_jiffy is calibrated at between 200MHz and
> > > 300MHz.
> > >
> > >
> > > I'm welcome to any suggestions for how to address this. It sorta
> > > feels like it would be a common thing to have a temporary PLL during
> > > the transition, ...
> >
> > We definitely do that on Tegra for some cpufreq transitions.
>
> Ouch... If this is a common strategy to use a third frequency during a
> transition phase, especially if that frequency is way off (800MHz vs
> 200-300MHz) then it is something the cpufreq layer must capture and
> advertise.
Of course if only the loops_per_jiffy scaling does care about frequency
changes these days, and if in those cases udelay() can instead be moved
to a timer source on those hick-up prone platforms, then all this is
fairly theoretical and may not be worth pursuing.
Nicolas
next prev parent reply other threads:[~2014-05-13 23:29 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-07 23:23 [PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems Doug Anderson
2014-05-08 10:41 ` Viresh Kumar
2014-05-08 15:25 ` Doug Anderson
2014-05-08 16:04 ` Nicolas Pitre
2014-05-08 16:41 ` Doug Anderson
2014-05-08 17:43 ` Nicolas Pitre
2014-05-08 18:06 ` Doug Anderson
2014-05-08 19:59 ` Nicolas Pitre
2014-05-08 20:55 ` Russell King - ARM Linux
2014-05-09 0:02 ` Doug Anderson
2014-05-09 0:23 ` Russell King - ARM Linux
2014-05-09 4:41 ` Doug Anderson
2014-05-08 19:22 ` Russell King - ARM Linux
2014-05-08 20:12 ` Nicolas Pitre
2014-05-08 20:39 ` John Stultz
2014-05-08 20:52 ` Russell King - ARM Linux
2014-05-09 1:37 ` Nicolas Pitre
2014-05-09 4:43 ` Doug Anderson
2014-05-09 9:18 ` [PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems# Russell King - ARM Linux
2014-05-09 18:00 ` Nicolas Pitre
2014-05-09 18:22 ` Russell King - ARM Linux
2014-05-09 21:05 ` Nicolas Pitre
2014-05-12 23:51 ` Doug Anderson
2014-05-13 21:50 ` Doug Anderson
2014-05-13 22:15 ` Stephen Warren
2014-05-13 23:15 ` Nicolas Pitre
2014-05-13 23:29 ` Nicolas Pitre [this message]
2014-05-13 23:36 ` Russell King - ARM Linux
2014-05-14 21:42 ` Doug Anderson
2014-05-15 6:12 ` Viresh Kumar
2014-05-09 9:25 ` [PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems Viresh Kumar
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