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From: Dexuan Cui <>
To: Thomas Gleixner <>,
	'Saeed Mahameed' <>,
	'Leon Romanovsky' <>
Cc: "''" <>,
	"''" <>,
	"''" <>,
	Haiyang Zhang <>,
	"''" <>
Subject: RE: [5.14-rc1] mlx5_core receives no interrupts with maxcpus=8
Date: Sun, 29 Aug 2021 20:11:33 +0000	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <87tuj9guzq.ffs@tglx>

> From: Thomas Gleixner <>
> Sent: Saturday, August 28, 2021 1:44 PM
> >> I tried the kernel parameter "intremap=nosid,no_x2apic_optout,nopost"
> but
> >> it didn't help. Only "intremap=off" can work round the no interrupt issue.
> >>
> >> When the no interrupt issue happens, irq 209's effective_affinity_list is 5.
> >> I modified modify_irte() to print the irte->low, irte->high, and I also printed
> >> the irte_index for irq 209, and they were all normal to me, and they were
> >> exactly the same in the bad case and the good case -- it looks like, with
> >> "intremap=on maxcpus=8", MSI-X on CPU5 can't work for the NIC device
> >> (MSI-X on CPU5 works for other devices like a NVMe controller) , and
> somehow
> >> "onlining and then offlining CPU 8~31" can "fix" the issue, which is really
> weird.
> Just for the record: maxcpus=N is a dangerous boot option as it leaves
> the non brought up CPUs in a state where they can be hit by MCE
> broadcasting without being able to act on it. Which means you're
> operating the system out of spec.

I didn't know about this. Thanks for the reply! 

> According to your debug output the interrupt in question belongs to the
> INTEL-IR-3 interrupt domain, which means it hangs of IOMMU3, aka DMAR
> unit 3.
> To which DMAR/remap unit are the other unaffected devices connected to?
>         tglx

With maxcpus=8, on CPU 5, the NIC receives no interrupt, but a NVMe
interrupt ("INTEL-IR-6") on the CPU works, and two "IOAT" interrupts 
("INTEL-IR-7") also work.

Except the NIC, the only IRQs connected to the faulty IOMMU3 are
irq33 and irq34:

root@lsg-gen7-a:~# cat /sys/kernel/debug/irq/irqs/33
handler:  handle_fasteoi_irq
device:   (null)
status:   0x00004100
istate:   0x00000000
ddepth:   1
wdepth:   0
dstate:   0x3503a000
node:     1
affinity: 0-103
effectiv: 0
domain:  IO-APIC-18
 hwirq:   0x0
 chip:    IR-IO-APIC
  flags:   0x10
    domain:  INTEL-IR-3
     hwirq:   0x0
     chip:    INTEL-IR
      flags:   0x0
        domain:  VECTOR
         hwirq:   0x21
         chip:    APIC
          flags:   0x0
         Vector:     0
         Target:     0
         move_in_progress: 0
         is_managed:       0
         can_reserve:      1
         has_reserved:     1
         cleanup_pending:  0

root@lsg-gen7-a:~# cat /sys/kernel/debug/irq/irqs/34
handler:  handle_edge_irq
device:   0000:d7:00.0
status:   0x00004000
istate:   0x00000000
ddepth:   0
wdepth:   0
dstate:   0x37408200
node:     1
affinity: 0-7
effectiv: 1
domain:  INTEL-IR-MSI-3-3
 hwirq:   0x6b80000
 chip:    IR-PCI-MSI
  flags:   0x30
    domain:  INTEL-IR-3
     hwirq:   0x10000
     chip:    INTEL-IR
      flags:   0x0
        domain:  VECTOR
         hwirq:   0x22
         chip:    APIC
          flags:   0x0
         Vector:    34
         Target:     1
         move_in_progress: 0
         is_managed:       0
         can_reserve:      1
         has_reserved:     0
         cleanup_pending:  0

root@lsg-gen7-a:~# lspci |grep d7:00.0
d7:00.0 PCI bridge: Intel Corporation Sky Lake-E PCI Express Root Port A (rev 07)

irq 33 doesn't appear in /proc/interupts.
irq 34 in /proc/interupts also receives no interrupts.

So it looks like IOMMU3 is somehow not working at all
with maxcpus=8. "onlining and offlining CPU 8~31" can
somehow "fix" it. :-) I'm not sure if this is a kernel issue
or firmware issue.


  reply	other threads:[~2021-08-29 20:14 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <draft-87h7fa1m37.ffs@tglx>
2021-08-28 20:44 ` Thomas Gleixner
2021-08-29 20:11   ` Dexuan Cui [this message]
2021-07-15  0:38 Dexuan Cui
2021-07-15  1:11 ` Dexuan Cui
2021-07-18  9:12   ` Leon Romanovsky
2021-07-19 20:17     ` Saeed Mahameed
2021-07-19 20:33       ` Dexuan Cui
2021-07-21 21:16         ` Thomas Gleixner
2021-08-18 21:08           ` Dexuan Cui
2021-08-19 20:41             ` Dexuan Cui

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