linux-kernel - Re: [PATCH] intel_idle: mention assumption that wbinvd is not needed

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Message-ID: <alpine.LNX.2.20.13.2010121410490.15808@monopod.intra.ispras.ru>
Date:   Mon, 12 Oct 2020 14:14:27 +0300 (MSK)
From:   Alexander Monakov <amonakov@...ras.ru>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
cc:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] intel_idle: mention assumption that wbinvd is not
 needed

On Mon, 12 Oct 2020, Rafael J. Wysocki wrote:

> > @@ -20,7 +20,11 @@
> >   * All CPUs have same idle states as boot CPU
> >   *
> >   * Chipset BM_STS (bus master status) bit is a NOP
> > - *     for preventing entry into deep C-stats
> > + *     for preventing entry into deep C-states
> > + *
> > + * CPU will flush caches as needed when entering a C-state via MWAIT
> 
> I would rephrase this to mention that the above actually is an assumption.

This comment block is by itself a list of assumptions. It begins with heading
"Design Assumptions" and then lists two assumptions. This patch adds a third
one.

With that clarified, do you still need me to change this hunk?

> 
> > + *     (in contrast to entering ACPI C3, where acpi_idle driver is
> 
> And mentioning acpi_idle here is not needed; it would be sufficient to
> say something like "in which case the WBINVD instruction needs to be
> executed to flush the caches".

I see, thanks, I will change this for v2 once the above is cleared up.

Thanks.
Alexander