linux-kernel - Re: [PATCH 2/3] irqchip/gic-v3-its: Postpone LPI pending table freeing and memreserve

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Message-ID: <878ryhb9l2.wl-maz@kernel.org>
Date:   Mon, 25 Oct 2021 12:57:45 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH 2/3] irqchip/gic-v3-its: Postpone LPI pending table freeing and memreserve

On Sun, 24 Oct 2021 16:51:53 +0100,
Valentin Schneider <valentin.schneider@....com> wrote:
> 
> What we could do instead is only have a PREALLOCATED flag (or RESERVED; in
> any case just one rather than two) set in its_cpu_init_lpis(), and ensure
> each CPU only ever executes the body of the callback exactly once.
> 
>   if (already_booted())
>       return 0;
> 
>   if (PREALLOCATED)
>       its_free_pending_table();
>   else
>       gic_reserve_range();
> 
>   out:
>     // callback removal faff here
>     return 0;
> 
> Unfortunately, the boot CPU will already be present in
> cpus_booted_once_mask when this is first invoked for the BP, so AFAICT we'd
> need some new tracking utility (either a new RDIST_LOCAL flag or a separate
> cpumask).
> 
> WDYT?

It'd certainly look saner. You may even be able to take advantage of
the fact that the boot CPU is always 0.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.