linux-kernel - Re: [PATCH] cpuidle: menu: allow state 0 to be disabled

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Date:   Thu, 29 Jun 2017 22:57:33 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        "Gautham R . Shenoy" <ego@...ux.vnet.ibm.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: menu: allow state 0 to be disabled

On Mon, Jun 26, 2017 at 7:38 AM, Nicholas Piggin <npiggin@...il.com> wrote:
> The menu driver does not allow state0 to be disabled completely.
> If it is disabled but other enabled states don't meet latency
> requirements, it is still used.
>
> Fix this by starting with the first enabled idle state. Fall back
> to state 0 if no idle states are enabled (arguably this should be
> -EINVAL if it is attempted, but this is the minimal fix).
>
> Acked-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin@...il.com>
> ---
>
> Hi Rafael,

Hi Nick,

> This patch is helpful when measuring power draw of polling,
> latency cost of idle states, etc. Please consider merging if
> you agree.

I have a slight concern about x86 where state0 is mapped to polling
and the way it is used in general stems from that.

Still, I guess we can try and see if this causes any problems to
happen in practice, so I'm going to apply it.

Thanks,
Rafael