linux-kernel - Re: [ARM64] Printing IRQ stack usage information

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Date:   Fri, 16 Nov 2018 13:31:51 -0500
From:   valdis.kletnieks@...edu
To:     Pintu Agarwal <pintu.ping@...il.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        kernelnewbies@...nelnewbies.org,
        Jungseok Lee <jungseoklee85@...il.com>,
        catalin.marinas@....com, will.deacon@....com,
        Takahiro Akashi <takahiro.akashi@...aro.org>,
        mark.rutland@....com, Sungjinn Chung <barami97@...il.com>
Subject: Re: [ARM64] Printing IRQ stack usage information

On Fri, 16 Nov 2018 23:13:48 +0530, Pintu Agarwal said:
> On Fri, Nov 16, 2018 at 10:16 PM <valdis.kletnieks@...edu> wrote:

> > Congrats. You just re-invented DEBUG_STACK_USAGE, which just keeps a high-water mark
> > for stack usage.
>
> So, you mean to say, my implementation is good enough to get the
> irq_stack usage, from the interrupt handler ?

No - your code doesn't keep a high-water mark (which should probably be
hooked into the IRQ exit code.

> But my concern is that if I dump it from irq handler, I will get
> information only for the current cpu.
> How do I store and get the information for all the cpu from the boot time ?

Make the high-water mark a per-cpu variable.

> From where do I call my dump_irq_stack_info() [some where during the
> entry/exit part of the irq handler], so that I could dump information
> for all the handler at boot time itself ?

No, you don't do a dump-stack during entry/exit.  You just maintain a high-water
value in the exit, and then you create a /proc/something or similar that when
read does a 'foreach CPU do print_high_water_irq'.

> Like I would to capture these information:
> - What was the name of the handler ?
> - Which cpu was executing it ?
> - How much irq stack (max value, same like high water mark) were used
> at that time ?

First, do the easy part and find out if you even *care* once you see actual
numbers.  If your IRQ stack is 8K but you never use more than 2500 bytes,
do you *really* care about the name of the handler anymore?

Also, see the code for /proc/interrupts to see how it keeps track of the
interrupts per CPU - maybe all you need to do is change each entry from
a 'count' to 'count, highwater'.

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