linux-kernel - Re: [PATCH v4 1/2] arm64: Introduce IRQ stack

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Message-ID: <20151008102520.GA10912@dhcppc13.redhat.com>
Date:	Thu, 8 Oct 2015 15:55:20 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	Jungseok Lee <jungseoklee85@...il.com>
Cc:	catalin.marinas@....com, will.deacon@....com,
	linux-arm-kernel@...ts.infradead.org, james.morse@....com,
	takahiro.akashi@...aro.org, mark.rutland@....com,
	barami97@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] arm64: Introduce IRQ stack

Hi Jungseok,

On 07/10/2015:03:28:11 PM, Jungseok Lee wrote:
> Currently, kernel context and interrupts are handled using a single
> kernel stack navigated by sp_el1. This forces a system to use 16KB
> stack, not 8KB one. This restriction makes low memory platforms suffer
> from memory pressure accompanied by performance degradation.

How will it behave on 64K Page system? There, it would take atleast 64K per cpu,
right?

> +int alloc_irq_stack(unsigned int cpu)
> +{
> +	void *stack;
> +
> +	if (per_cpu(irq_stacks, cpu).stack)
> +		return 0;
> +
> +	stack = (void *)__get_free_pages(THREADINFO_GFP, THREAD_SIZE_ORDER);

Above would not compile for 64K pages as THREAD_SIZE_ORDER is only defined for
non 64K. This need to be fixed.

~Pratyush
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