linux-kernel - Re: [PATCH 2/2][v2] cpuidle-haltpoll: Build as module by default

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Message-ID: <CAJZ5v0gXSUdFeHajUcjV-eh3eW1aRoJ8Yvp9J95czQg0cMetTA@mail.gmail.com>
Date:   Thu, 8 Dec 2022 12:42:51 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     "Li,Rongqing" <lirongqing@...du.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "jpoimboe@...nel.org" <jpoimboe@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/2][v2] cpuidle-haltpoll: Build as module by default

On Thu, Dec 8, 2022 at 3:32 AM Li,Rongqing <lirongqing@...du.com> wrote:
>
>
> > > Allow user to unload it in running
> >
> > Just like that?  And corrupt things left and right while at it?
> >
> > No way.
> >
> > And why do you need this?
>
> Cpuidle-haltpoll can not improve performance for all cases, like when guest has mwait, unixbench shows a small performance drop;
> So change it as module, user can insmod this drivers and rmmod this driver at run time

That is problematic, because in the mainline Linux kernel (which is
what we are talking about here) there is no support for modular
cpuidle governors.

Also, there is an interface for switching cpuidle governors at run
time already, so why can 't it be used to address this case?

> And some downstream os, centos and ubuntu build it module

Well, it's their problem.