linux-kernel - Re: [PATCH v2] x86/ACPI/boot: Improve __acpi_acquire_global

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Date:   Wed, 22 Mar 2023 21:34:16 +0100
From:   Uros Bizjak <ubizjak@...il.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>, x86@...nel.org,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Len Brown <lenb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] x86/ACPI/boot: Improve __acpi_acquire_global_lock

On Wed, Mar 22, 2023 at 7:34 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 3/22/23 11:24, Rafael J. Wysocki wrote:
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > or please let me know if you want me to pick this up (in which case it
> > will require an ACK from one of the x86 maintainers).
>
> I'll pull it into x86/acpi.  I'm kinda shocked the compiler is so
> clueless, but this makes the C code more readable anyway.  Win/win, I guess.

Please note that the return form __acpi_{acquire,release}_global_lock
is actually used as bool:

acenv.h:

int __acpi_acquire_global_lock(unsigned int *lock);
int __acpi_release_global_lock(unsigned int *lock);

#define ACPI_ACQUIRE_GLOBAL_LOCK(facs, Acq) \
((Acq) = __acpi_acquire_global_lock(&facs->global_lock))

#define ACPI_RELEASE_GLOBAL_LOCK(facs, Acq) \
((Acq) = __acpi_release_global_lock(&facs->global_lock))

evglock.c:

acpi_status acpi_ev_acquire_global_lock(u16 timeout)
{
    ...
    u8 acquired = FALSE;
    ...
    ACPI_ACQUIRE_GLOBAL_LOCK(acpi_gbl_FACS, acquired);
    if (acquired) ...
}

acpi_status acpi_ev_release_global_lock(void)
{
    u8 pending = FALSE;
    ...
   ACPI_RELEASE_GLOBAL_LOCK(acpi_gbl_FACS, pending);
   if (pending) ...
}

These functions are also defined for ia64, so I didn't want to change
the return value. But ia64 is going to be retired, and this opens the
optimization opportunity.

Uros.