On Thu, 25 Nov 2021 at 15:13, Maulik Shah [off-list ref] wrote:

Hi Peter,

On 11/25/2021 3:21 PM, Peter Zijlstra wrote:

quoted

On Thu, Nov 25, 2021 at 02:44:36PM +0530, Maulik Shah wrote:

quoted

Export cpu_idle_poll_ctrl() so that module drivers can use same.

This does not seem like a really safe interface to expose to the
world.

Thanks for the review.

Keeping the cpuidle enabled from boot up may delay/increase the boot up
time.
Below is our use case to force cpuidle to stay in cpu_idle_poll().

We keep cpuidle disabled from boot up using "nohlt" option of kernel
command line which internally sets cpu_idle_force_poll = 1;
and once the device bootup reaches till certain point (for example the
android homescreen is up) userspace may notify a
vendor module driver which can invoke cpu_idle_poll_ctrl(false); to come
out of poll mode.
So vendor module driver needs cpu_idle_poll_ctrl() exported symbol.

Waiting for the homescreen can be considered as rather late, from the
kernel boot progress point of view.

That said, I am wondering if a similar improvement can be achieved by
just allowing WFI (thus no deeper idle states) until homescreen? If
so, that can be quite easily achieved by modularizing the cpuidle-psci
driver.

[...]

Kind regards
Uffe