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Re: [PATCH v3] genirq: Machine-parsable version of /proc/interrupts

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On Thu, Sep 8, 2016 at 6:00 PM, Randy Dunlap <rdunlap@infradead.org> wrote:
> On 09/08/16 13:25, Craig Gallek wrote:
>> From: Craig Gallek <kraig@google.com>
>>
>> Add struct kobject to struct irq_desc to allow for easy export
>> to sysfs.  This allows for much simpler userspace-parsing of
>> the information contained in struct irq_desc.
>>
>> Note that sysfs is not available at the time of early irq initialization.
>> These interrupts are accounted for using a postcore_initcall callback.
>>
>> Examples:
>>   /sys/kernel/irq/18/actions: i801_smbus,ehci_hcd:usb1,uhci_hcd:usb7
>>   /sys/kernel/irq/18/chip_name:       IR-IO-APIC
>>   /sys/kernel/irq/18/hwirq:           18
>>   /sys/kernel/irq/18/name:            fasteoi
>>   /sys/kernel/irq/18/per_cpu_count:   0,0
>>   /sys/kernel/irq/18/type:            level
>>
>>   /sys/kernel/irq/25/actions: ahci0
>>   /sys/kernel/irq/25/chip_name:       IR-PCI-MSI
>>   /sys/kernel/irq/25/hwirq:           512000
>>   /sys/kernel/irq/25/name:            edge
>>   /sys/kernel/irq/25/per_cpu_count:   29036,0
>>   /sys/kernel/irq/25/type:            edge
>
> Thanks for the update.
>
> One concern:
>
> This per_cpu_count is for online CPUs only.
> How does this help when the online CPUs change?
>
> E.g., above could be for CPUs 1 and 5.
> The next time that it is read it could be for CPUs 0 and 3.
> Seems that it could be confusing even for software reading it.

Thanks for the feedback. I imagine most use cases for this will simply
add up all the values to obtain a total.  There's not a lot of use for
the individual elements unless you additionally know something about
the CPU id layout, interrupt pinning, and/or CPU online state.  The
/proc/interrupts interface has this same issue, but additionally uses
column headers.  There's really know way to give a similar consistent
view of all of this data using multiple sysfs files.  Given this lack
of atomicity, across files, I don't think it's unreasonable for the
counter order to change when the system's online CPUs change.

The only alternative I could imagine would be to include a header row
in this file listing the CPU ids as a parallel list.  I think this
goes against the standard sysfs file format, though...

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[PATCH v2] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-08 19:40 +0200
  Re: [PATCH v2] genirq: Machine-parsable version of /proc/interrupts Randy Dunlap <rdunlap@infradead.org> - 2016-09-08 20:00 +0200
  [PATCH v3] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-08 22:30 +0200
    Re: [PATCH v3] genirq: Machine-parsable version of /proc/interrupts Randy Dunlap <rdunlap@infradead.org> - 2016-09-09 00:10 +0200
      Re: [PATCH v3] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-09 00:20 +0200
        Re: [PATCH v3] genirq: Machine-parsable version of  /proc/interrupts Thomas Gleixner <tglx@linutronix.de> - 2016-09-09 14:50 +0200
  [PATCH v4] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-09 18:30 +0200
    Re: [PATCH v4] genirq: Machine-parsable version of  /proc/interrupts Thomas Gleixner <tglx@linutronix.de> - 2016-09-10 01:30 +0200
    [PATCH v5] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-12 16:20 +0200
      Re: [PATCH v5] genirq: Machine-parsable version of  /proc/interrupts Thomas Gleixner <tglx@linutronix.de> - 2016-09-13 17:00 +0200
      [PATCH v6] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-13 18:20 +0200
        Re: [PATCH v6] genirq: Machine-parsable version of  /proc/interrupts Thomas Gleixner <tglx@linutronix.de> - 2016-09-14 15:40 +0200
          Re: [PATCH v6] genirq: Machine-parsable version of /proc/interrupts Craig Gallek <kraigatgoog@gmail.com> - 2016-09-14 16:00 +0200
        [tip:irq/core] genirq: Expose interrupt information through sysfs tip-bot for Craig Gallek <tipbot@zytor.com> - 2016-09-14 15:40 +0200

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