Re: [PATCH RFC 00/14] Add the BFQ I/O Scheduler to blk-mq

[Paolo Valente]

> Il giorno 06 mar 2017, alle ore 08:43, Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx> ha scritto:
> 
> On 2017.03.04 at 17:01 +0100, Paolo Valente wrote:
>> Hi,
>> at last, here is my first patch series meant for merging. It adds BFQ
>> to blk-mq. Don't worry, in this message I won't bore you again with
>> the wonderful properties of BFQ :)
> 
> I gave BFQ a quick try. Unfortunately it hangs when I try to delete
> btrfs snapshots:
> 
> root       124  0.0  0.0      0     0 ?        D    07:19   0:03 [btrfs-cleaner]  
> root       125  0.0  0.0      0     0 ?        D    07:19   0:00 [btrfs-transacti]
> 
> [ 4372.880116] sysrq: SysRq : Show Blocked State
> [ 4372.880125]   task                        PC stack   pid father
> [ 4372.880148] btrfs-cleaner   D    0   124      2 0x00000000
> [ 4372.880156] Call Trace:
> [ 4372.880166]  ? __schedule+0x160/0x7c0
> [ 4372.880174]  ? io_schedule+0x64/0xe0
> [ 4372.880179]  ? wait_on_page_bit+0x7a/0x100
> [ 4372.880183]  ? devm_memunmap+0x40/0x40
> [ 4372.880189]  ? read_extent_buffer_pages+0x25c/0x2c0
> [ 4372.880195]  ? run_one_async_done+0xc0/0xc0
> [ 4372.880200]  ? btree_read_extent_buffer_pages+0x60/0x2e0
> [ 4372.880206]  ? read_tree_block+0x2c/0x60
> [ 4372.880211]  ? read_block_for_search.isra.38+0xec/0x3a0
> [ 4372.880217]  ? btrfs_search_slot+0x214/0xbc0
> [ 4372.880221]  ? lookup_inline_extent_backref+0xfb/0x8c0
> [ 4372.880225]  ? __btrfs_free_extent.isra.74+0xe9/0xdc0
> [ 4372.880231]  ? btrfs_merge_delayed_refs+0x57/0x6e0
> [ 4372.880235]  ? __btrfs_run_delayed_refs+0x60d/0x1340
> [ 4372.880239]  ? btrfs_run_delayed_refs+0x64/0x280
> [ 4372.880243]  ? btrfs_should_end_transaction+0x3b/0xa0
> [ 4372.880247]  ? btrfs_drop_snapshot+0x3b2/0x800
> [ 4372.880251]  ? __schedule+0x168/0x7c0
> [ 4372.880254]  ? btrfs_clean_one_deleted_snapshot+0xa4/0xe0
> [ 4372.880259]  ? cleaner_kthread+0x13a/0x180
> [ 4372.880264]  ? btree_invalidatepage+0xc0/0xc0
> [ 4372.880268]  ? kthread+0x144/0x180
> [ 4372.880272]  ? kthread_flush_work_fn+0x20/0x20
> [ 4372.880277]  ? ret_from_fork+0x23/0x30
> [ 4372.880280] btrfs-transacti D    0   125      2 0x00000000
> [ 4372.880285] Call Trace:
> [ 4372.880290]  ? __schedule+0x160/0x7c0
> [ 4372.880295]  ? io_schedule+0x64/0xe0
> [ 4372.880300]  ? wait_on_page_bit_common.constprop.57+0x160/0x180
> [ 4372.880303]  ? devm_memunmap+0x40/0x40
> [ 4372.880307]  ? __filemap_fdatawait_range+0xd3/0x140
> [ 4372.880311]  ? clear_state_bit.constprop.82+0xf7/0x180
> [ 4372.880315]  ? __clear_extent_bit.constprop.79+0x138/0x3c0
> [ 4372.880319]  ? filemap_fdatawait_range+0x9/0x60
> [ 4372.880323]  ? __btrfs_wait_marked_extents.isra.18+0xc1/0x100
> [ 4372.880327]  ? btrfs_write_and_wait_marked_extents.constprop.23+0x49/0x80
> [ 4372.880331]  ? btrfs_commit_transaction+0x8e1/0xb00
> [ 4372.880334]  ? join_transaction.constprop.24+0x10/0xa0
> [ 4372.880340]  ? wake_bit_function+0x60/0x60
> [ 4372.880345]  ? transaction_kthread+0x185/0x1a0
> [ 4372.880350]  ? btrfs_cleanup_transaction+0x500/0x500
> [ 4372.880354]  ? kthread+0x144/0x180
> [ 4372.880358]  ? kthread_flush_work_fn+0x20/0x20
> [ 4372.880362]  ? ret_from_fork+0x23/0x30
> [ 4372.880367] ntpd            D    0   175      1 0x00000004
> [ 4372.880372] Call Trace:
> [ 4372.880375]  ? __schedule+0x160/0x7c0
> [ 4372.880379]  ? schedule_preempt_disabled+0x2d/0x80
> [ 4372.880383]  ? __mutex_lock.isra.5+0x17b/0x4c0
> [ 4372.880386]  ? wait_current_trans+0x15/0xc0
> [ 4372.880391]  ? btrfs_free_path+0xe/0x20
> [ 4372.880395]  ? btrfs_pin_log_trans+0x14/0x40
> [ 4372.880400]  ? btrfs_rename2+0x28e/0x19c0
> [ 4372.880404]  ? path_init+0x187/0x3e0
> [ 4372.880407]  ? unlazy_walk+0x4b/0x100
> [ 4372.880410]  ? terminate_walk+0x8d/0x100
> [ 4372.880414]  ? filename_parentat+0x1e9/0x2c0
> [ 4372.880420]  ? __kmalloc_track_caller+0xc4/0x100
> [ 4372.880424]  ? vfs_rename+0x33f/0x7e0
> [ 4372.880428]  ? SYSC_renameat2+0x53c/0x680
> [ 4372.880433]  ? entry_SYSCALL_64_fastpath+0x13/0x94
> [ 4372.880437] fcron           D    0   178      1 0x00000000
> [ 4372.880441] Call Trace:
> [ 4372.880445]  ? __schedule+0x160/0x7c0
> [ 4372.880448]  ? schedule_preempt_disabled+0x2d/0x80
> [ 4372.880452]  ? __mutex_lock.isra.5+0x17b/0x4c0
> [ 4372.880458]  ? pagevec_lookup_tag+0x18/0x20
> [ 4372.880462]  ? btrfs_log_dentry_safe+0x4cd/0xac0
> [ 4372.880466]  ? btrfs_start_transaction+0x249/0x460
> [ 4372.880470]  ? btrfs_sync_file+0x288/0x3c0
> [ 4372.880475]  ? btrfs_file_write_iter+0x3a9/0x4e0
> [ 4372.880479]  ? vfs_write+0x26c/0x2c0
> [ 4372.880483]  ? SyS_write+0x3d/0xa0
> [ 4372.880486]  ? SyS_fchown+0x7b/0xa0
> [ 4372.880491]  ? entry_SYSCALL_64_fastpath+0x13/0x94
> [ 4372.880508] kworker/u8:8    D    0   759      2 0x00000000
> [ 4372.880518] Workqueue: btrfs-submit btrfs_submit_helper
> [ 4372.880520] Call Trace:
> [ 4372.880524]  ? __schedule+0x160/0x7c0
> [ 4372.880529]  ? io_schedule+0x64/0xe0
> [ 4372.880534]  ? blk_mq_get_tag+0x212/0x320
> [ 4372.880538]  ? wake_bit_function+0x60/0x60
> [ 4372.880544]  ? __blk_mq_alloc_request+0x11/0x1c0
> [ 4372.880548]  ? blk_mq_sched_get_request+0x17e/0x220
> [ 4372.880553]  ? blk_sq_make_request+0xd3/0x4c0
> [ 4372.880557]  ? blk_mq_sched_dispatch_requests+0x104/0x160
> [ 4372.880561]  ? generic_make_request+0xc3/0x2e0
> [ 4372.880564]  ? submit_bio+0x58/0x100
> [ 4372.880569]  ? run_scheduled_bios+0x1a6/0x500
> [ 4372.880574]  ? btrfs_worker_helper+0x129/0x1c0
> [ 4372.880580]  ? process_one_work+0x1bc/0x400
> [ 4372.880585]  ? worker_thread+0x42/0x540
> [ 4372.880588]  ? __schedule+0x168/0x7c0
> [ 4372.880592]  ? process_one_work+0x400/0x400
> [ 4372.880596]  ? kthread+0x144/0x180
> [ 4372.880600]  ? kthread_flush_work_fn+0x20/0x20
> [ 4372.880605]  ? ret_from_fork+0x23/0x30
> 
> I could get it going again by running:
> echo "mq-deadline" > /sys/block/sdb/queue/scheduler
> 

Hi Markus,
thanks for testing BFQ.  And sorry for replying only now.  Before
replying I have tried to reproduce the failure, or to understand
somehow the link between the failure and BFQ (unfortunately, no BFQ
function is preset in your stack trace). Unfortunately at no avail.

I hope that your failure was caused by one of the bugs that I have
fixed from the previous submission.  So, if you could try the new
patch series [1] when you have time to, I would really appreciate
that.

Thanks,
Paolo

[1] https://lkml.org/lkml/2017/3/31/393

> --
> Markus