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SubjectRe: system hung up when offlining CPUs
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On 09/13/2017 09:33 AM, Thomas Gleixner wrote:
> On Wed, 13 Sep 2017, Kashyap Desai wrote:
>>> On 09/12/2017 08:15 PM, YASUAKI ISHIMATSU wrote:
>>>> + linux-scsi and maintainers of megasas
>
>>>>> In my server, IRQ#66-89 are sent to CPU#24-29. And if I offline
>>>>> CPU#24-29, I/O does not work, showing the following messages.
>
> ....
>
>>> This indeed looks like a problem.
>>> We're going to great lengths to submit and complete I/O on the same CPU,
>>> so
>>> if the CPU is offlined while I/O is in flight we won't be getting a
>>> completion for
>>> this particular I/O.
>>> However, the megasas driver should be able to cope with this situation;
>>> after
>>> all, the firmware maintains completions queues, so it would be dead easy
>>> to
>>> look at _other_ completions queues, too, if a timeout occurs.
>> In case of IO timeout, megaraid_sas driver is checking other queues as well.
>> That is why IO was completed in this case and further IOs were resumed.
>>
>> Driver complete commands as below code executed from
>> megasas_wait_for_outstanding_fusion().
>> for (MSIxIndex = 0 ; MSIxIndex < count; MSIxIndex++)
>> complete_cmd_fusion(instance, MSIxIndex);
>>
>> Because of above code executed in driver, we see only one print as below in
>> this logs.
>> megaraid_sas 0000:02:00.0: [ 0]waiting for 2 commands to complete for scsi0
>>
>> As per below link CPU hotplug will take care- "All interrupts targeted to
>> this CPU are migrated to a new CPU"
>> https://www.kernel.org/doc/html/v4.11/core-api/cpu_hotplug.html
>>
>> BTW - We are also able reproduce this issue locally. Reason for IO timeout
>> is -" IO is completed, but corresponding interrupt did not arrived on Online
>> CPU. Either missed due to CPU is in transient state of being OFFLINED. I am
>> not sure which component should take care this."
>>
>> Question - "what happens once __cpu_disable is called and some of the queued
>> interrupt has affinity to that particular CPU ?"
>> I assume ideally those pending/queued Interrupt should be migrated to
>> remaining online CPUs. It should not be unhandled if we want to avoid such
>> IO timeout.
>
> Can you please provide the following information, before and after
> offlining the last CPU in the affinity set:
>
> # cat /proc/irq/$IRQNUM/smp_affinity_list
> # cat /proc/irq/$IRQNUM/effective_affinity
> # cat /sys/kernel/debug/irq/irqs/$IRQNUM
>
> The last one requires: CONFIG_GENERIC_IRQ_DEBUGFS=y

Here are one irq's info of megasas:

- Before offline CPU
/proc/irq/70/smp_affinity_list
24-29

/proc/irq/70/effective_affinity
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,3f000000

/sys/kernel/debug/irq/irqs/70
handler: handle_edge_irq
status: 0x00004000
istate: 0x00000000
ddepth: 0
wdepth: 0
dstate: 0x00609200
IRQD_ACTIVATED
IRQD_IRQ_STARTED
IRQD_MOVE_PCNTXT
IRQD_AFFINITY_SET
IRQD_AFFINITY_MANAGED
node: 1
affinity: 24-29
effectiv: 24-29
pending:
domain: INTEL-IR-MSI-0-2
hwirq: 0x100018
chip: IR-PCI-MSI
flags: 0x10
IRQCHIP_SKIP_SET_WAKE
parent:
domain: INTEL-IR-0
hwirq: 0x400000
chip: INTEL-IR
flags: 0x0
parent:
domain: VECTOR
hwirq: 0x46
chip: APIC
flags: 0x0

- After offline CPU#24-29
/proc/irq/70/smp_affinity_list
29

/proc/irq/70/effective_affinity
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,20000000

/sys/kernel/debug/irq/irqs/70
handler: handle_edge_irq
status: 0x00004000
istate: 0x00000000
ddepth: 1
wdepth: 0
dstate: 0x00a39000
IRQD_IRQ_DISABLED
IRQD_IRQ_MASKED
IRQD_MOVE_PCNTXT
IRQD_AFFINITY_SET
IRQD_AFFINITY_MANAGED
IRQD_MANAGED_SHUTDOWN
node: 1
affinity: 29
effectiv: 29
pending:
domain: INTEL-IR-MSI-0-2
hwirq: 0x100018
chip: IR-PCI-MSI
flags: 0x10
IRQCHIP_SKIP_SET_WAKE
parent:
domain: INTEL-IR-0
hwirq: 0x400000
chip: INTEL-IR
flags: 0x0
parent:
domain: VECTOR
hwirq: 0x46
chip: APIC
flags: 0x0

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
>
> tglx
>

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