Re: [PATCH] ARM: smp: Fix missing backtrace IPI statics
From: Jinjie Ruan
Date: Thu Aug 01 2024 - 21:44:18 EST
On 2024/8/2 9:39, Jinjie Ruan wrote:
>
>
> On 2024/8/2 0:36, Russell King (Oracle) wrote:
>> On Thu, Aug 01, 2024 at 05:40:22PM +0800, Jinjie Ruan wrote:
>>> It is similar to ARM64 commit 916b93f4e865 ("arm64: smp: Fix missing IPI
>>> statistics"), commit 56afcd3dbd19 ("ARM: Allow IPIs to be handled as normal
>>> interrupts") set CPU_BACKTRACE IPI "IRQ_HIDDEN" flag but not show it in
>>> show_ipi_list(), which cause the interrupt kstat_irqs accounting
>>> is missing in display.
>>
>> I don't see why this needs to be included. If this IPI fires, it means
>> that the kernel has suffered a lockup and is probably not very useful.
>> So the chances of being able to read out from /proc/interrupts a non-
>> zero "CPU backtrace interrupts" figure is highly unlikely.
>
> It is more of a change than a bug.
>
> If we reset the arm32 code to before commit 56afcd3dbd19 ("ARM: Allow
> IPIs to be handled as normal interrupts"), the backtrace IPI statics is
> shown ok as below, but after that it is missing:
Sorry, there is some mistake here, the original result has no backtrace
IPI statics.
>
> / # cat /proc/interrupts
> CPU0
> 24: 6 GIC-0 34 Level timer
> 25: 469 GIC-0 29 Level twd
> 26: 61 GIC-0 75 Edge virtio0
> 29: 8 GIC-0 44 Level kmi-pl050
> 30: 118 GIC-0 45 Level kmi-pl050
> 31: 0 GIC-0 36 Level rtc-pl031
> 32: 0 GIC-0 41 Level mmci-pl18x (cmd)
> 33: 0 GIC-0 42 Level mmci-pl18x (pio)
> 34: 0 GIC-0 92 Level arm-pmu
> 35: 0 GIC-0 93 Level arm-pmu
> 36: 0 GIC-0 94 Level arm-pmu
> 37: 0 GIC-0 95 Level arm-pmu
> 39: 15 GIC-0 37 Level uart-pl011
> IPI0: 0 CPU wakeup interrupts
> IPI1: 0 Timer broadcast interrupts
> IPI2: 0 Rescheduling interrupts
> IPI3: 0 Function call interrupts
> IPI4: 0 CPU stop interrupts
> IPI5: 0 IRQ work interrupts
> IPI6: 0 completion interrupts
> IPI7: 0 CPU backtrace interrupts
>
>
>>
>> So, I don't see much point to this change.
>>