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

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Date:	Tue, 8 Sep 2015 23:59:50 +0900
From:	Jungseok Lee <jungseoklee85@...il.com>
To:	AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:	James Morse <james.morse@....com>,
	linux-arm-kernel@...ts.infradead.org,
	"linux-kernel@...r.kernel.org Mailing List" 
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: kernel: Use a separate stack for irq interrupts.

On Sep 8, 2015, at 10:45 AM, AKASHI Takahiro wrote:
> Jungseok,

Hi Akashi,

> On 09/08/2015 01:34 AM, Jungseok Lee wrote:
>> On Sep 8, 2015, at 1:06 AM, James Morse wrote:
>>> 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…)
>> 
>> When I enabled the feature, all entries had *0* size except the last entry.
>> It can be reproduced easily as looking in debugs:/tracing/stack_trace.
> 
> I'm afraid that you have not applied one of patches in my RFC:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/355919.html

My description is not clear. Whenever I use a stack tracer, I always put your
RFC and Steve's stack tracer fix on top of my tree.

Best Regards
Jungseok Lee--
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