linux-kernel - Re: [PATCH] arm64: kernel: Use a separate stack for irq interrupts.

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Message-ID: <55EDB5FB.8060800@arm.com>
Date:	Mon, 07 Sep 2015 17:06:19 +0100
From:	James Morse <james.morse@....com>
To:	Jungseok Lee <jungseoklee85@...il.com>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kernel: Use a separate stack for irq interrupts.

On 07/09/15 16:48, Jungseok Lee wrote:
> On Sep 7, 2015, at 11:36 PM, James Morse wrote:
> 
> Hi James,
> 
>> Having to handle interrupts on top of an existing kernel stack means the
>> kernel stack must be large enough to accomodate both the maximum kernel
>> usage, and the maximum irq handler usage. Switching to a different stack
>> when processing irqs allows us to make the stack size smaller.
>>
>> Maximum kernel stack usage (running ltp and generating usb+ethernet
>> interrupts) was 7256 bytes. With this patch, the same workload gives
>> a maximum stack usage of 5816 bytes.
> 
> I'd like to know how to measure the max stack depth.
> AFAIK, a stack tracer on ftrace does not work well. Did you dump a stack
> region and find or track down an untouched region? 

I enabled the 'Trace max stack' option under menuconfig 'Kernel Hacking' ->
'Tracers', then looked in debugfs:/tracing/stack_max_size.

What problems did you encounter?
(I may be missing something...)


Thanks,

James
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