Re: Hard and soft lockups with FIO and LTP runs on a large system

[Bharata B Rao <bharata@amd.com>]

On 07-Jul-24 4:12 AM, Yu Zhao wrote:
>> Some experiments tried
>> ======================
>> 1) When MGLRU was enabled many soft lockups were observed, no hard
>> lockups were seen for 48 hours run. Below is once such soft lockup.
<snip>
>> Below preemptirqsoff trace points to preemption being disabled for more
>> than 10s and the lock in picture is lruvec spinlock.
> 
> Also if you could try the other patch (mglru.patch) please. It should
> help reduce unnecessary rotations from deactivate_file_folio(), which
> in turn should reduce the contention on the LRU lock for MGLRU.

Thanks. With mglru.patch on a MGLRU-enabled system, the below latency 
trace record is no longer seen for a 30hr workload run.

> 
>>       # tracer: preemptirqsoff
>>       #
>>       # preemptirqsoff latency trace v1.1.5 on 6.10.0-rc3-mglru-irqstrc
>>       # --------------------------------------------------------------------
>>       # latency: 10382682 us, #4/4, CPU#128 | (M:desktop VP:0, KP:0, SP:0
>> HP:0 #P:512)
>>       #    -----------------
>>       #    | task: fio-2701523 (uid:0 nice:0 policy:0 rt_prio:0)
>>       #    -----------------
>>       #  => started at: deactivate_file_folio
>>       #  => ended at:   deactivate_file_folio
>>       #
>>       #
>>       #                    _------=> CPU#
>>       #                   / _-----=> irqs-off/BH-disabled
>>       #                  | / _----=> need-resched
>>       #                  || / _---=> hardirq/softirq
>>       #                  ||| / _--=> preempt-depth
>>       #                  |||| / _-=> migrate-disable
>>       #                  ||||| /     delay
>>       #  cmd     pid     |||||| time  |   caller
>>       #     \   /        ||||||  \    |    /
>>            fio-2701523 128...1.    0us$: deactivate_file_folio
>> <-deactivate_file_folio
>>            fio-2701523 128.N.1. 10382681us : deactivate_file_folio
>> <-deactivate_file_folio
>>            fio-2701523 128.N.1. 10382683us : tracer_preempt_on
>> <-deactivate_file_folio
>>            fio-2701523 128.N.1. 10382691us : <stack trace>
>>        => deactivate_file_folio
>>        => mapping_try_invalidate
>>        => invalidate_mapping_pages
>>        => invalidate_bdev
>>        => blkdev_common_ioctl
>>        => blkdev_ioctl
>>        => __x64_sys_ioctl
>>        => x64_sys_call
>>        => do_syscall_64
>>        => entry_SYSCALL_64_after_hwframe

However the contention now has shifted to inode_hash_lock. Around 55 
softlockups in ilookup() were observed:

# tracer: preemptirqsoff
#
# preemptirqsoff latency trace v1.1.5 on 6.10.0-rc3-trnmglru
# --------------------------------------------------------------------
# latency: 10620430 us, #4/4, CPU#260 | (M:desktop VP:0, KP:0, SP:0 HP:0 
#P:512)
#    -----------------
#    | task: fio-3244715 (uid:0 nice:0 policy:0 rt_prio:0)
#    -----------------
#  => started at: ilookup
#  => ended at:   ilookup
#
#
#                    _------=> CPU#
#                   / _-----=> irqs-off/BH-disabled
#                  | / _----=> need-resched
#                  || / _---=> hardirq/softirq
#                  ||| / _--=> preempt-depth
#                  |||| / _-=> migrate-disable
#                  ||||| /     delay
#  cmd     pid     |||||| time  |   caller
#     \   /        ||||||  \    |    /
      fio-3244715 260...1.    0us$: _raw_spin_lock <-ilookup
      fio-3244715 260.N.1. 10620429us : _raw_spin_unlock <-ilookup
      fio-3244715 260.N.1. 10620430us : tracer_preempt_on <-ilookup
      fio-3244715 260.N.1. 10620440us : <stack trace>
=> _raw_spin_unlock
=> ilookup
=> blkdev_get_no_open
=> blkdev_open
=> do_dentry_open
=> vfs_open
=> path_openat
=> do_filp_open
=> do_sys_openat2
=> __x64_sys_openat
=> x64_sys_call
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

It appears that scalability issues with inode_hash_lock has been brought 
up multiple times in the past and there were patches to address the same.

https://lore.kernel.org/all/20231206060629.2827226-9-david@fromorbit.com/
https://lore.kernel.org/lkml/20240611173824.535995-2-mjguzik@gmail.com/

CC'ing FS folks/list for awareness/comments.

Regards,
Bharata.