linux-kernel - Re: [PATCH v4 19/19] irqdomain: Switch to per-domain locking

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Date:   Wed, 18 Jan 2023 14:09:22 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Johan Hovold <johan@...nel.org>
Cc:     Johan Hovold <johan+linaro@...nel.org>,
        Marc Zyngier <maz@...nel.org>, x86@...nel.org,
        platform-driver-x86@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hsin-Yi Wang <hsinyi@...omium.org>,
        Mark-PK Tsai <mark-pk.tsai@...iatek.com>
Subject: Re: [PATCH v4 19/19] irqdomain: Switch to per-domain locking

On Wed, Jan 18 2023 at 10:51, Johan Hovold wrote:
> On Tue, Jan 17, 2023 at 10:50:39PM +0100, Thomas Gleixner wrote:
>> On Mon, Jan 16 2023 at 14:50, Johan Hovold wrote:
>> > The IRQ domain structures are currently protected by the global
>> > irq_domain_mutex. Switch to using more fine-grained per-domain locking,
>> > which may potentially speed up parallel probing somewhat.
>> 
>> Does it or not?
>> 
>> If not then why adding all this churn for no real value?
>
> It probably doesn't make much difference, but Marc wanted per-domain
> locking:
>
>     > I'd really like to avoid a global mutex. At the very least this should
>     > be a per-domain mutex, otherwise this will serialise a lot more than
>     > what is needed.

Sure it serializes more than what is needed, but the real question is
whether it matters. If it does not matter then I prefer KISS over a just
because we can optimization.

Thanks,

        tglx