linux-kernel - Re: [RFC PATCH 0/3] Implement IRQ stack on ARM64

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Message-ID: <55EDA040.90208@arm.com>
Date:	Mon, 07 Sep 2015 15:33:36 +0100
From:	James Morse <james.morse@....com>
To:	Jungseok Lee <jungseoklee85@...il.com>
CC:	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/3] Implement IRQ stack on ARM64

On 04/09/15 15:23, Jungseok Lee wrote:
> ARM64 kernel allocates 16KB kernel stack when creating a process. In case
> of low memory platforms with tough workloads on userland, this order-2
> allocation request reaches to memory pressure and performance degradation
> simultaenously since VM page allocator falls into slowpath frequently,
> which triggers page reclaim and compaction.
> 
> I believe that one of the best solutions is to reduce kernel stack size.
> According to the following data from stack tracer with some fixes, [1],
> a separate IRQ stack would greatly help to decrease a kernel stack depth.
>

Hi Jungseok Lee,

I was working on a similar patch for irq stack, (patch as a follow up email).

I suggest we work together on a single implementation. I think the only
major difference is that you're using sp_el0 as a temporary register to
store a copy of the stack-pointer to find struct thread_info, whereas I was
copying it between stacks (ends up as 2x ldp/stps), which keeps the change
restricted to irq_stack setup code.

We should get some feedback as to which approach is preferred.


Thanks,

James Morse


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