Re: [PATCH] cpuidle: Add the shallow governors

[Roman Kagan <rkagan@amazon.de>]

On Thu, Oct 08, 2026 at 07:29:43PM +0100, Christian Loehle wrote:
> On 10/8/26 19:17, Christian Loehle wrote:
> > On 10/8/26 19:06, Roman Kagan wrote:
> >> The idle states offered by a platform trade wakeup latency for energy
> >> savings, and there are situations where the trade is not worth making:
> >> while a latency-sensitive workload is running, or during a live update
> >> via kexec, where everything from the outgoing kernel stopping the
> >> workload to the incoming kernel resuming it is downtime, and deep idle
> >> states may lengthen it.
> >>
> >> The mechanisms currently available for that are all one-way.
> >> cpuidle.off=1, idle=poll and idle=halt can only be requested in the
> >> kernel command line and cannot be undone, and the PM QoS interfaces
> >> (/dev/cpu_dma_latency and the per-CPU pm_qos_resume_latency_us
> >> attribute) can only be used once user space is up, so they cannot cover
> >> the boot of the incoming kernel.
> > 
> > You can also disable all but the shallowest idle state in sysfs:
> > echo 1 > /sys/devices/system/cpu/cpuX/cpuidle/stateX/disable
> > 
> 
> And I'd probably prefer having that exposed via the cmdline rather than
> two separate governors...

Doing this cmdline configuration per-cpu per-state is non-realistic.  I
guess you mean a single option that would express a policy, like "for
all cpus in the system, disable all but the shallowest state" or "...
all but the shallowest non-polling".  But policy is exactly what
governors are for.

Why exactly does having two more separate simple, narrow-purpose
governors sound wrong to you?

Thanks,
Roman.