linux-kernel - Re: [PATCH v5 19/27] irqchip/gic-v3: Remove acknowledge loop

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Message-ID: <ee78b536-6a87-52c7-16c4-292f7ecbe61a@arm.com>
Date:   Wed, 3 Oct 2018 10:26:00 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Julien Thierry <julien.thierry@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, daniel.thompson@...aro.org,
        joel@...lfernandes.org, mark.rutland@....com,
        christoffer.dall@....com, james.morse@....com,
        catalin.marinas@....com, will.deacon@....com,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH v5 19/27] irqchip/gic-v3: Remove acknowledge loop

On 28/08/18 16:51, Julien Thierry wrote:
> Multiple interrupts pending for a CPU is actually rare. Doing an
> acknowledge loop does not give much better performance or even can
> deteriorate them.
> 
> Do not loop when an interrupt has been acknowledged, just return
> from interrupt and wait for another one to be raised.
> 
> Tested-by: Daniel Thompson <daniel.thompson@...aro.org>
> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jason Cooper <jason@...edaemon.net>
> Cc: Marc Zyngier <marc.zyngier@....com>
> ---
>   drivers/irqchip/irq-gic-v3.c | 65 +++++++++++++++++++++-----------------------
>   1 file changed, 31 insertions(+), 34 deletions(-)

It would probably be valuable to do the same thing for GICv1/v2, where 
the MMIO access can be even more costly.

In the meantime, I've queued this for 4.20.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...