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

[Yu Zhao <yuzhao@google.com>]

On Wed, Jul 10, 2024 at 6:04 AM Bharata B Rao <bharata@amd.com> wrote:
>
> 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.

Glad to hear. Will post a patch and add you as reported/tested-by.

> >
> >>       # 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:

This one is from fs/blk, so I'll leave it to those experts.

> # 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.