linux-kernel - Re: [PATCH] arm64: smp: Fix missing IPI statistics

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Date: Fri, 14 Jun 2024 10:48:08 +0800
From: Jinjie Ruan <ruanjinjie@...wei.com>
To: Doug Anderson <dianders@...omium.org>
CC: <catalin.marinas@....com>, <will@...nel.org>, <mark.rutland@....com>,
	<swboyd@...omium.org>, <sumit.garg@...aro.org>, <frederic@...nel.org>,
	<scott@...amperecomputing.com>, <misono.tomohiro@...itsu.com>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: smp: Fix missing IPI statistics



On 2024/6/8 0:02, Doug Anderson wrote:
> Hi,
> 
> On Fri, Jun 7, 2024 at 12:45 AM Jinjie Ruan <ruanjinjie@...wei.com> wrote:
>>
>> commit 83cfac95c018 ("genirq: Allow interrupts to be excluded from
>> /proc/interrupts") is to avoid IPIs appear twice in /proc/interrupts.
>> But the commit 331a1b3a836c ("arm64: smp: Add arch support for backtrace
>> using pseudo-NMI") and commit 2f5cd0c7ffde("arm64: kgdb: Implement
>> kgdb_roundup_cpus() to enable pseudo-NMI roundup") set CPU_BACKTRACE and
>> KGDB_ROUNDUP IPIs "IRQ_HIDDEN" flag but not show them in
>> arch_show_interrupts(), which cause the interrupt kstat_irqs accounting
>> is missing in display.
>>
>> Fixes: 331a1b3a836c ("arm64: smp: Add arch support for backtrace using pseudo-NMI")
>> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
>> ---
>>  arch/arm64/kernel/smp.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> While I won't object to your patch if everyone agrees that we want it,

Hello, What's everyone's opinion?

> fully excluding "cpu backtrace" and "kgdb roundup" from
> /proc/interrupts was more of a design decision than a bug. Those two
> IPIs are really special cases and not something that I'd expect anyone
> to care about knowing the count of. Keeping them out of
> "/proc/interrupts" just avoids noise. I'd also note that I believe
> arm32 makes the same design choice for "cpu backtrace".

Yes, arm32 is same as arm64.

> 
> In any case, if we truly think people want the count of these IPIs
> then it feels like we should report them in arch_show_interrupts()
> where we can give them a nice string.

That's a good idea.

> 
> -Doug