linux-kernel - Re: [PATCH v3 3/3] intel_idle: Provide enter

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Message-ID: <e1f08d24-2896-418e-891a-d707d6ba50cf@intel.com>
Date: Tue, 12 Nov 2024 08:07:00 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Patryk Wlazlyn <patryk.wlazlyn@...ux.intel.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 rafael.j.wysocki@...el.com, len.brown@...el.com,
 artem.bityutskiy@...ux.intel.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH v3 3/3] intel_idle: Provide enter_dead() handler for SRF

On 11/12/24 03:28, Rafael J. Wysocki wrote:
> On Tue, Nov 12, 2024 at 12:18 PM Patryk Wlazlyn
> <patryk.wlazlyn@...ux.intel.com> wrote:
>>> This series has said multiple times how the old algorithm is wrong.  But
>>> it never actually _fixed_ the bad algorithm, only worked around it.
>>>
>>> Does mwait_play_dead() itself need to get fixed?
>> I don't think so. The old algorithm gives fairly good heuristic for computing
>> the mwait hint for the deepest cstate. Even though it's not guaranteed to work,
>> it does work on most of the platforms that don't early return. I think we should
>> leave it, but prefer idle_driver.
> IOW, as a fallback mechanism, it is as good as it gets.
> 
> As the primary source of information though, not quite.

Could we also work to make this a bit more clear when it should be used
and where the primary sources of information are?