RE: [5.14-rc1] mlx5_core receives no interrupts with maxcpus=8

[Dexuan Cui]

> From: Dexuan Cui
> Sent: Wednesday, July 14, 2021 5:39 PM
> To: netdev@xxxxxxxxxxxxxxx; x86@xxxxxxxxxx
> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [5.14-rc1] mlx5_core receives no interrupts with maxcpus=8
> 
> Hi all,
> I'm seeing a strange "no MSI-X interrupt" issue with the Mellanox NIC
> driver on a physical Linux host [1], if I only enable part of the CPUs.
> 
> The physical host has 104 logical processors (2 sockets, and each socket
> has 26 cores with HT enabled). By default, the Mellanox driver works fine
> when Linux boots up.
> 
> If I only use 1, 2, 32, 64, 96 processors by the Linux kernel parameter
> "maxcpus=X" or "nr_cpus=X", everthing still works fine.
> 
> However, if the Linux host OS only uses 4, 8 or 16 processors, the
> mlx5_core driver fails to load as it can not receive interrupt when
> creating EQ (maxcpus=8 or 16), or the driver can load but it reports a
> timeout error when I try to bring the NIC up (maxcpus=4). This issue is
> a 100% repro.
> 
> For example, with "maxcpus=8", I get the below timeout error when trying
> to load mlx5_core:
> 
> # modprobe mlx5_core
> [ 1475.716688] mlx5_core 0000:d8:00.0: firmware version: 16.25.8352
> [ 1475.722742] mlx5_core 0000:d8:00.0: 126.016 Gb/s available PCIe
> bandwidth (8.0 GT/s PCIe x16 link)
> [ 1475.991398] mlx5_core 0000:d8:00.0: E-Switch: Total vports 2, per vport:
> max uc(1024) max mc(16384)
> 
> [ 1537.020001] mlx5_core 0000:d8:00.0: mlx5_cmd_eq_recover:245:(pid 1416):
> Recovered 1 EQEs on cmd_eq
> [ 1537.028969] mlx5_core 0000:d8:00.0:
> wait_func_handle_exec_timeout:1062:(pid 1416): cmd[0]: CREATE_EQ(0x301)
> recovered after timeout
> [ 1598.460003] mlx5_core 0000:d8:00.0: mlx5_cmd_eq_recover:245:(pid 1416):
> Recovered 1 EQEs on cmd_eq
> [ 1598.468978] mlx5_core 0000:d8:00.0:
> wait_func_handle_exec_timeout:1062:(pid 1416): cmd[0]: CREATE_EQ(0x301)
> recovered after timeout
> [ 1659.900010] mlx5_core 0000:d8:00.0: mlx5_cmd_eq_recover:245:(pid 1416):
> Recovered 1 EQEs on cmd_eq
> [ 1659.908987] mlx5_core 0000:d8:00.0:
> wait_func_handle_exec_timeout:1062:(pid 1416): cmd[0]: CREATE_EQ(0x301)
> recovered after timeout
> [ 1721.340006] mlx5_core 0000:d8:00.0: mlx5_cmd_eq_recover:245:(pid 1416):
> Recovered 1 EQEs on cmd_eq
> [ 1721.348989] mlx5_core 0000:d8:00.0:
> wait_func_handle_exec_timeout:1062:(pid 1416): cmd[0]: CREATE_EQ(0x301)
> recovered after timeout
> 
> When this happens, the mlx5_core driver is stuck with the below
> call-trace, waiting for some interrupt:
> 
> # ps aux |grep modprobe
> root        1416  0.0  0.0  11024  1472 ttyS0    D+   08:08   0:00
> modprobe mlx5_core
> root        1480  0.0  0.0   6440   736 pts/0    S+   08:15   0:00
> grep --color=auto modprobe
> 
> # cat /proc/1416/stack
> [<0>] cmd_exec+0x8a7/0x9b0 [mlx5_core]
> [<0>] mlx5_cmd_exec+0x24/0x50 [mlx5_core]
> [<0>] create_map_eq+0x2a6/0x380 [mlx5_core]
> [<0>] mlx5_eq_table_create+0x504/0x710 [mlx5_core]
> [<0>] mlx5_load+0x52/0x130 [mlx5_core]
> [<0>] mlx5_init_one+0x1cc/0x250 [mlx5_core]
> [<0>] probe_one+0x1d3/0x2a0 [mlx5_core]
> [<0>] local_pci_probe+0x45/0x80
> [<0>] pci_device_probe+0x10f/0x1c0
> [<0>] really_probe+0x1c1/0x3b0
> [<0>] __driver_probe_device+0x109/0x180
> [<0>] driver_probe_device+0x23/0xa0
> [<0>] __driver_attach+0xbd/0x160
> [<0>] bus_for_each_dev+0x7c/0xc0
> [<0>] driver_attach+0x1e/0x20
> [<0>] bus_add_driver+0x152/0x1f0
> [<0>] driver_register+0x74/0xd0
> [<0>] __pci_register_driver+0x68/0x70
> [<0>] init+0x6b/0x1000 [mlx5_core]
> [<0>] do_one_initcall+0x46/0x1d0
> [<0>] do_init_module+0x62/0x250
> [<0>] load_module+0x2503/0x2730
> [<0>] __do_sys_finit_module+0xbf/0x120
> [<0>] __x64_sys_finit_module+0x1a/0x20
> [<0>] do_syscall_64+0x38/0xc0
> [<0>] entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> To make the issue even weirder, when the issue happens (e.g. when Linux
> only uses 8 processors), if I manually bring CPU #8~#31 online [2] and
> then bring them offline [3], the Mellanox driver will work fine!
> 
> This is a x86-64 host. Is it possibe that the IOMMU Interrrupt Remapping
> is not proprely set up with maxcpus=4, 8 and 16?
> 
> The above tests were done with the recent Linux v5.14-rc1 kernel. I also
> tried Ubuntu 20.04's kernel "5.4.0-77-generic", and the Mellanox driver
> exhibits exactly the same issue.
> 
> I have Linux/Windows dual-boot on this physical machine, and Windows
> doesn't have the issue when I let it only use 4, 8 and 16 processors.
> So this looks like somehow the issue is specific to Linux.
> 
> Can someone please shed some light on this strange issue? I'm ready
> to provide more logs if needed. Thanks!
> 
> PS, the physical machine has 4 NVMe controllers and 4 Broadcom NICs,
> which are not affected by maxcpus=4, 8, and 16.
> 
> [1] This is the 'lspci' output of the Mellanox NIC:
> d8:00.0 Ethernet controller: Mellanox Technologies MT27800 Family
> [ConnectX-5]
>         Subsystem: Mellanox Technologies MT27800 Family [ConnectX-5]
>         Flags: bus master, fast devsel, latency 0, IRQ 33, NUMA node 1
>         Memory at f8000000 (64-bit, prefetchable) [size=32M]
>         Expansion ROM at fbe00000 [disabled] [size=1M]
>         Capabilities: [60] Express Endpoint, MSI 00
>         Capabilities: [48] Vital Product Data
>         Capabilities: [9c] MSI-X: Enable+ Count=64 Masked-
>         Capabilities: [c0] Vendor Specific Information: Len=18 <?>
>         Capabilities: [40] Power Management version 3
>         Capabilities: [100] Advanced Error Reporting
>         Capabilities: [150] Alternative Routing-ID Interpretation (ARI)
>         Capabilities: [180] Single Root I/O Virtualization (SR-IOV)
>         Capabilities: [1c0] Secondary PCI Express
>         Kernel driver in use: mlx5_core
>         Kernel modules: mlx5_core
> 00: b3 15 17 10 46 05 10 00 00 00 00 02 08 00 00 00
> 10: 0c 00 00 f8 00 00 00 00 00 00 00 00 00 00 00 00
> 20: 00 00 00 00 00 00 00 00 00 00 00 00 b3 15 80 00
> 30: 00 00 e0 fb 60 00 00 00 00 00 00 00 ff 01 00 00
> 
> [2] for i in `seq 8 31`;  do echo 1 >  /sys/devices/system/cpu/cpu$i/online;
> done
> [3] for i in `seq 8 31`;  do echo 0 >  /sys/devices/system/cpu/cpu$i/online;
> done
> 
> Thanks,
> -- Dexuan

(+ the linux-pci list)

It turns out that adding "intremap=off" can work around the issue!

The root cause is still not clear yet. I don't know why Windows is good here.

Thanks,
Dexuan