linux-kernel - Re: [PATCH 4.4-rc5 v22 1/4] irqchip: gic: Optimize locking in gic_raise

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Message-ID: <568E76BE.3010702@arm.com>
Date:	Thu, 07 Jan 2016 14:31:26 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Daniel Thompson <daniel.thompson@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Russell King <linux@....linux.org.uk>
CC:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	John Stultz <john.stultz@...aro.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	patches@...aro.org, linaro-kernel@...ts.linaro.org,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Dirk Behme <dirk.behme@...bosch.com>,
	Daniel Drake <drake@...lessm.com>,
	Dmitry Pervushin <dpervushin@...il.com>,
	Tim Sander <tim@...eglstein.org>,
	Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH 4.4-rc5 v22 1/4] irqchip: gic: Optimize locking in gic_raise_softirq

On 20/12/15 20:52, Daniel Thompson wrote:
> Currently gic_raise_softirq() is locked using irq_controller_lock.
> This lock is primarily used to make register read-modify-write sequences
> atomic but gic_raise_softirq() uses it instead to ensure that the
> big.LITTLE migration logic can figure out when it is safe to migrate
> interrupts between physical cores.
> 
> This is sub-optimal in closely related ways:
> 
> 1. No locking at all is required on systems where the b.L switcher is
>    not configured.
> 
> 2. Finer grain locking can be used on systems where the b.L switcher is
>    present.
> 
> This patch resolves both of the above by introducing a separate finer
> grain lock and providing conditionally compiled inlines to lock/unlock
> it.
> 
> Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Jason Cooper <jason@...edaemon.net>
> Cc: Russell King <linux@....linux.org.uk>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Acked-by: Nicolas Pitre <nicolas.pitre@...aro.org>

Acked-by: Marc Zyngier <marc.zyngier@....com>

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