linux-kernel - Re: [PATCH 00/28] PM: QoS: Get rid of unuseful code and rework CPU latency QoS interface

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Date:   Thu, 13 Feb 2020 12:40:05 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/28] PM: QoS: Get rid of unuseful code and rework CPU
 latency QoS interface

On Wed, Feb 12, 2020 at 5:09 AM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> Hi All,
>
> This series of patches is based on the observation that after commit
> c3082a674f46 ("PM: QoS: Get rid of unused flags") the only global PM QoS class
> in use is PM_QOS_CPU_DMA_LATENCY, but there is still a significant amount of
> code dedicated to the handling of global PM QoS classes in general.  That code
> takes up space and adds overhead in vain, so it is better to get rid of it.
>
> Moreover, with that unuseful code removed, the interface for adding QoS
> requests for CPU latency becomes inelegant and confusing, so it is better to
> clean it up.
>
> Patches [01/28-12/28] do the first part described above, which also includes
> some assorted cleanups of the core PM QoS code that doesn't go away.
>
> Patches [13/28-25/28] rework the CPU latency QoS interface (in the classic
> "define stubs, migrate users, change the API proper" manner), patches
> [26-27/28] update the general comments and documentation to match the code
> after the previous changes and the last one makes the CPU latency QoS depend
> on CPU_IDLE (because cpuidle is the only user of its target value today).
>
> The majority of the patches in this series don't change the functionality of
> the code at all (at least not intentionally).
>
> Please refer to the changelogs of individual patches for details.

Hi Rafael,

Nice cleanup to the code and docs.

I've reviewed the series, and briefly tested it by setting latencies
from userspace. Can we not remove the debugfs interface? It is a quick
way to check the global cpu latency clamp on the system from userspace
without setting up tracepoints or writing a program to read
/dev/cpu_dma_latency.

Except for patch 01/28 removing the debugfs interface, please feel to add my

Reviewed-by: Amit Kucheria <amit.kucheria@...aro.org>
Tested-by: Amit Kucheria <amit.kucheria@...aro.org>

Regards,
Amit