Re: 2.6.37: Multi-second I/O latency while untarring

Andrew Lutomirski
2011-02-12T00:35:25Z

On Fri, Feb 11, 2011 at 10:44 AM, Chris Mason <chris.mason@oracle.com> wrote:
> Excerpts from Andrew Lutomirski's message of 2011-02-11 10:08:52 -0500:
>> As I type this, I have an ssh process running that's dumping data into
>> a fifo at high speed (maybe 500Mbps) and a tar process that's
>> untarring from the same fifo onto btrfs.  The btrfs fs is mounted -o
>> space_cache,compress.  This machine has 8GB ram, 8 logical cores, and
>> a fast (i7-2600) CPU, so it's not an issue with the machine struggling
>> under load.
>>
>> Every few tens of seconds, my system stalls for several seconds.
>> These stalls cause keyboard input to be lost, firefox to hang, etc.
>>
>> Setting tar's ionice priority to best effort / 7 or to idle makes no difference.
>>
>> ionice idle and queue_depth = 1 on the disk (a slow 2TB WD) also makes
>> no difference.
>>
>> max_sectors_kb = 64 in addition to the above doesn't help either.
>>
>> latencytop shows regular instances of 2-7 *second* latency, variously
>> in sync_page, start_transaction, btrfs_start_ordered_extent, and
>> do_get_write_access (from jbd2 on my ext4 root partition).
>>
>> echo 3 >drop_caches gave me 7 GB free RAM.  I still had stalls when
>> 4-5 GB were still free (so it shouldn't be a problem with important
>> pages being evicted).
>>
>> In case it matters, all of my partitions are on LVM on dm-crypt, but
>> this machine has AES-NI so the overhead from that should be minimal.
>> In fact, overall CPU usage is only about 10%.
>>
>> What gives?  I thought this stuff was supposed to be better on modern kernels.
>
> We can tell more if you post the full traces from latencytop.  I have a
> patch here for latencytop that adds a -c mode, which dumps the traces
> out to a text files.
>
> http://oss.oracle.com/~mason/latencytop.patch
>
> Based on what you have here, I think it's probably a latency problem
> between btrfs and the dm-crypt stuff.  How easily can setup a test
> partition without dm-crypt?

Done, on the same physical disk as before. The latency is just as
bad. On this test, I wrote a total of 3.1G, which is under half of my
RAM. That should rule out lots of VM issues. latencytop trace below.

The impression I get (from watching the disk activity light) is that
the disk is mostly idle but every now and then writes out a ton of
data. While it's writing, the system often becomes unusable.

P.S. How bad is this? I got it on both disks.
btrfs: free space inode generation (0) did not match free space cache
generation (11070) for block group 1103101952

=============== Fri Feb 11 19:30:57 2011
Globals: Cause Maximum Percentage
Writing a page to disk 2009.0 msec 19.7 %
fsync() on a file (type 'F' for details) 612.2 msec 5.0 %
synchronous write 573.6 msec 1.8 %
Page fault 57.3 msec 0.7 %
Writing buffer to disk (synchronous) 45.2 msec 0.1 %
Unlinking file 12.6 msec 0.0 %
Waiting for event (select) 5.0 msec 22.3 %
Reading from a pipe 5.0 msec 29.9 %
Waiting for event (poll) 5.0 msec 17.8 %
Process details:
Process kthreadd (2) Total: 1.9 msec
kthreadd kernel thread 1.9 msec 100.0 %
kthreadd kernel_thread_helper
Process ksoftirqd/0 (3) Total: 18.5 msec
[run_ksoftirqd] 4.0 msec 100.0 %
run_ksoftirqd kthread kernel_thread_helper
Process ksoftirqd/1 (10) Total: 19.6 msec
[run_ksoftirqd] 4.9 msec 100.0 %
run_ksoftirqd kthread kernel_thread_helper
Process kworker/0:1 (11) Total: 556.3 msec
. 5.0 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process ksoftirqd/2 (15) Total: 8.1 msec
[run_ksoftirqd] 2.9 msec 100.0 %
run_ksoftirqd kthread kernel_thread_helper
Process ksoftirqd/4 (23) Total: 11.2 msec
[run_ksoftirqd] 4.3 msec 100.0 %
run_ksoftirqd kthread kernel_thread_helper
Process scsi_eh_1 (62) Total: 38.8 msec
SCSI error handler 0.9 msec 39.9 %
scsi_error_handler kthread kernel_thread_helper
Executing internal ATA command 0.7 msec 60.1 %
ata_exec_internal_sg ata_exec_internal atapi_eh_request_sense
ata_eh_link_autopsy ata_eh_autopsy sata_pmp_error_handler
ahci_error_handler ata_scsi_error scsi_error_handler kthread
kernel_thread_helper
Process kworker/u:4 (69) Total: 616.5 msec
Creating block layer request 54.9 msec 77.8 %
get_request_wait __make_request generic_make_request
kcryptd_crypt_write_io_submit kcryptd_crypt process_one_work
worker_thread kthread kernel_thread_helper
. 5.0 msec 22.2 %
worker_thread kthread kernel_thread_helper
Process kworker/u:5 (70) Total: 1712.3 msec
Creating block layer request 492.8 msec 94.3 %
get_request_wait __make_request generic_make_request
kcryptd_io process_one_work worker_thread kthread
kernel_thread_helper
. 4.9 msec 5.7 %
worker_thread kthread kernel_thread_helper
Process kworker/7:1 (76) Total: 5.7 msec
. 4.8 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/5:1 (117) Total: 31.9 msec
. 4.9 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/6:1 (118) Total: 13.6 msec
. 4.9 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/1:1 (119) Total: 126.3 msec
. 4.9 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/4:1 (120) Total: 377.5 msec
. 5.0 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/2:1 (131) Total: 73.1 msec
. 4.9 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process kworker/3:1 (132) Total: 30.7 msec
. 4.9 msec 100.0 %
worker_thread kthread kernel_thread_helper
Process jbd2/dm-1-8 (372) Total: 137.4 msec
Writing buffer to disk (synchronous) 127.3 msec 92.8 %
sync_buffer __wait_on_buffer wait_on_buffer
jbd2_journal_commit_transaction kjournald2 kthread
kernel_thread_helper
Writing a page to disk 9.9 msec 7.2 %
sync_page wait_on_page_bit filemap_fdatawait_range
filemap_fdatawait jbd2_journal_commit_transaction kjournald2
kthread kernel_thread_helper
Process btrfs-worker-0 (828) Total: 4.6 msec
[worker_loop] 2.2 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-submit-0 (830) Total: 5.8 msec
[worker_loop] 2.3 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-delalloc- (831) Total: 1.1 msec
[worker_loop] 1.1 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-0 (833) Total: 69.1 msec
[worker_loop] 4.7 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (834) Total: 56.0 msec
[worker_loop] 4.5 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (835) Total: 19.8 msec
[worker_loop] 4.8 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-freespace (837) Total: 10.0 msec
[worker_loop] 1.4 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-transacti (841) Total: 3271.2 msec
Writing a page to disk 507.8 msec 89.5 %
sync_page __lock_page lock_page
extent_write_cache_pages.clone.11.clone.18 extent_writepages
btrfs_writepages do_writepages __filemap_fdatawrite_range
filemap_flush btrfs_run_ordered_operations
btrfs_commit_transaction transaction_kthread
Writing buffer to disk (synchronous) 305.5 msec 10.5 %
sync_buffer __wait_on_buffer write_dev_supers write_all_supers
write_ctree_super btrfs_commit_transaction transaction_kthread
kthread kernel_thread_helper
Process hald-addon-inpu (1347) Total: 5.4 msec
Waiting for event (poll) 5.0 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process hald-addon-stor (1362) Total: 48.2 msec
Opening file 3.5 msec 21.7 %
bd_prepare_to_claim bd_start_claiming blkdev_open
__dentry_open nameidata_to_filp do_last do_filp_open
do_sys_open sys_open system_call_fastpath
Executing raw SCSI command 1.2 msec 38.7 %
blk_execute_rq scsi_execute scsi_execute_req
sr_test_unit_ready sr_drive_status cdrom_ioctl sr_block_ioctl
__blkdev_driver_ioctl blkdev_ioctl block_ioctl do_vfs_ioctl
sys_ioctl
opening cdrom device 1.2 msec 33.4 %
blk_execute_rq scsi_execute scsi_execute_req
sr_test_unit_ready sr_media_change media_changed
cdrom_media_changed sr_block_media_changed check_disk_change
cdrom_open sr_block_open __blkdev_get
SCSI cdrom ioctl 0.6 msec 6.2 %
blk_execute_rq scsi_execute sr_do_ioctl sr_packet
cdrom_get_media_event sr_drive_status cdrom_ioctl
sr_block_ioctl __blkdev_driver_ioctl blkdev_ioctl block_ioctl
do_vfs_ioctl
Process Xorg (1533) Total: 4718.6 msec
Waiting for event (select) 5.0 msec 93.8 %
poll_schedule_timeout do_select core_sys_select sys_select
system_call_fastpath
[i915_do_wait_request] 4.3 msec 3.5 %
i915_do_wait_request i915_gem_object_wait_rendering
i915_gem_do_execbuffer.clone.29 i915_gem_execbuffer2 drm_ioctl
do_vfs_ioctl sys_ioctl system_call_fastpath
[__mutex_fastpath_lock_retval] 3.4 msec 2.7 %
__mutex_fastpath_lock_retval i915_mutex_lock_interruptible
i915_gem_pwrite_ioctl drm_ioctl do_vfs_ioctl sys_ioctl
system_call_fastpath
Waiting for TTY data 0.3 msec 0.0 %
flush_work flush_delayed_work tty_flush_to_ldisc
input_available_p n_tty_poll tty_poll do_select
core_sys_select sys_select system_call_fastpath
Process gnome-settings- (1857) Total: 18.1 msec
Waiting for event (poll) 3.9 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process flush-btrfs-1 (1865) Total: 0.7 msec
Writing a page to disk 0.1 msec 100.0 %
sync_page __lock_page lock_page
extent_write_cache_pages.clone.11.clone.18 extent_writepages
btrfs_writepages do_writepages writeback_single_inode
writeback_sb_inodes writeback_inodes_wb wb_writeback
wb_do_writeback
Process nautilus (1884) Total: 0.5 msec
Waiting for event (poll) 0.2 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process compiz (1893) Total: 650.6 msec
Waiting for event (poll) 5.0 msec 79.4 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
[i915_do_wait_request] 2.5 msec 20.2 %
i915_do_wait_request i915_gem_object_wait_rendering
i915_gem_do_execbuffer.clone.29 i915_gem_execbuffer2 drm_ioctl
do_vfs_ioctl sys_ioctl system_call_fastpath
[__mutex_fastpath_lock_retval] 1.0 msec 0.4 %
__mutex_fastpath_lock_retval i915_mutex_lock_interruptible
i915_gem_set_domain_ioctl drm_ioctl do_vfs_ioctl sys_ioctl
system_call_fastpath
Process wnck-applet (1927) Total: 2.6 msec
Waiting for event (poll) 0.7 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process udisks-daemon (2005) Total: 24.1 msec
Opening file 3.3 msec 53.0 %
bd_prepare_to_claim bd_start_claiming blkdev_open
__dentry_open nameidata_to_filp do_last do_filp_open
do_sys_open sys_open system_call_fastpath
opening cdrom device 1.2 msec 41.6 %
blk_execute_rq scsi_execute scsi_execute_req
sr_test_unit_ready sr_media_change media_changed
cdrom_media_changed sr_block_media_changed check_disk_change
cdrom_open sr_block_open __blkdev_get
Executing raw SCSI command 0.4 msec 5.4 %
blk_execute_rq scsi_execute scsi_execute_req
ioctl_internal_command.clone.3 scsi_set_medium_removal
sr_lock_door cdrom_release sr_block_release __blkdev_put
blkdev_put blkdev_close fput
Process btrfs-worker-3 (2097) Total: 1.1 msec
[worker_loop] 0.6 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-worker-4 (2098) Total: 0.4 msec
[worker_loop] 0.2 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process gtk-window-deco (2133) Total: 69.0 msec
Page fault 57.3 msec 83.1 %
sync_page wait_on_page_bit wait_on_page_locked
__lock_page_or_retry filemap_fault __do_fault handle_mm_fault
do_page_fault page_fault
Waiting for event (poll) 3.8 msec 16.9 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process gvfsd-trash (2152) Total: 495.5 msec
Waiting for event (poll) 5.0 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process gnome-terminal (2185) Total: 483.3 msec
Waiting for event (poll) 4.0 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process firefox (2426) Total: 5028.3 msec
Writing a page to disk 867.7 msec 48.5 %
sync_page wait_on_page_bit read_extent_buffer_pages
btree_read_extent_buffer_pages.clone.56 read_tree_block
read_block_for_search.clone.38 btrfs_search_slot
btrfs_lookup_csum __btrfs_lookup_bio_sums
btrfs_lookup_bio_sums btrfs_submit_bio_hook submit_one_bio

fsync() on a file (type 'F' for details) 612.2 msec 24.4 %
sync_page __lock_page lock_page
extent_write_cache_pages.clone.11.clone.18 extent_writepages
btrfs_writepages do_writepages __filemap_fdatawrite_range
filemap_write_and_wait_range vfs_fsync_range vfs_fsync
do_fsync
synchronous write 573.6 msec 11.4 %
start_transaction btrfs_join_transaction btrfs_dirty_inode
__mark_inode_dirty file_update_time btrfs_file_aio_write
do_sync_write vfs_write sys_write system_call_fastpath

Page fault 57.0 msec 2.9 %
sync_page wait_on_page_bit wait_on_page_locked
__lock_page_or_retry filemap_fault __do_fault handle_mm_fault
do_page_fault page_fault
Writing buffer to disk (synchronous) 45.2 msec 0.9 %
sync_buffer __wait_on_buffer ext4_find_entry ext4_lookup
d_alloc_and_lookup do_lookup do_last do_filp_open do_sys_open
sys_open system_call_fastpath
Unlinking file 12.6 msec 0.3 %
btrfs_tree_lock btrfs_search_slot btrfs_insert_empty_items
run_clustered_refs btrfs_run_delayed_refs
__btrfs_end_transaction btrfs_end_transaction_throttle
__unlink_end_trans btrfs_unlink vfs_unlink do_unlinkat
sys_unlink
Waiting for event (poll) 4.9 msec 5.9 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Userspace lock contention 4.9 msec 5.7 %
futex_wait_queue_me futex_wait do_futex sys_futex
system_call_fastpath
Process btrfs-delalloc- (2453) Total: 1.8 msec
[worker_loop] 1.1 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-wri (2454) Total: 44.7 msec
Writing a page to disk 31.1 msec 98.1 %
sync_page wait_on_page_bit read_extent_buffer_pages
btree_read_extent_buffer_pages.clone.56 read_tree_block
read_block_for_search.clone.38 btrfs_search_slot
btrfs_insert_empty_items alloc_reserved_file_extent.clone.57
run_clustered_refs btrfs_run_delayed_refs
__btrfs_end_transaction
[worker_loop] 0.7 msec 1.9 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-wri (2460) Total: 819.2 msec
Writing a page to disk 532.4 msec 99.8 %
sync_page __lock_page lock_page read_extent_buffer_pages
btree_read_extent_buffer_pages.clone.56 read_tree_block
reada_for_balance btrfs_search_slot btrfs_csum_file_blocks
add_pending_csums.clone.29 btrfs_finish_ordered_io
btrfs_writepage_end_io_hook
[worker_loop] 0.8 msec 0.2 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (2464) Total: 146.5 msec
[worker_loop] 4.7 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-genwork-0 (2573) Total: 2.1 msec
[worker_loop] 1.8 msec 87.6 %
worker_loop kthread kernel_thread_helper
[kthread_create] 0.1 msec 12.4 %
kthread_create __btrfs_start_workers btrfs_start_workers
start_new_worker_func worker_loop kthread kernel_thread_helper

Process btrfs-submit-0 (2574) Total: 2797.6 msec
Creating block layer request 484.7 msec 99.9 %
get_request_wait __make_request generic_make_request
submit_bio run_scheduled_bios pending_bios_fn worker_loop
kthread kernel_thread_helper
[worker_loop] 0.1 msec 0.1 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (2579) Total: 5.1 msec
[worker_loop] 1.9 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-wri (2580) Total: 146.3 msec
[worker_loop] 5.0 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-freespace (2581) Total: 0.4 msec
[worker_loop] 0.4 msec 100.0 %
worker_loop kthread kernel_thread_helper
Process btrfs-transacti (2583) Total: 479.7 msec
Writing buffer to disk (synchronous) 466.0 msec 97.2 %
sync_buffer __wait_on_buffer write_dev_supers write_all_supers
write_ctree_super btrfs_commit_transaction transaction_kthread
kthread kernel_thread_helper
Writing a page to disk 6.4 msec 2.8 %
sync_page wait_on_page_bit filemap_fdatawait_range
filemap_fdatawait filemap_write_and_wait btrfs_write_out_cache
btrfs_write_dirty_block_groups commit_cowonly_roots
btrfs_commit_transaction transaction_kthread kthread
kernel_thread_helper
Process ssh (2659) Total: 2559.8 msec
Waiting for event (select) 4.9 msec 100.0 %
poll_schedule_timeout do_select core_sys_select sys_select
system_call_fastpath
Process tar (2662) Total: 9364.3 msec
Reading from a pipe 5.0 msec 100.0 %
pipe_wait pipe_read do_sync_read vfs_read sys_read
system_call_fastpath
Process btrfs-endio-wri (2741) Total: 1.1 msec
[worker_loop] 1.0 msec 97.6 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (2742) Total: 2.4 msec
[worker_loop] 1.8 msec 99.1 %
worker_loop kthread kernel_thread_helper
Process btrfs-endio-met (2743) Total: 2.3 msec
[worker_loop] 1.8 msec 99.9 %
worker_loop kthread kernel_thread_helper
Process bash (2753) Total: 483.3 msec
Waiting for event (poll) 4.0 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process btrfs-endio-wri (2790) Total: 1.9 msec
kthreadd kernel thread 1.9 msec 100.0 %
kthreadd kernel_thread_helper
Process sudo (2792) Total: 483.3 msec
Waiting for event (poll) 4.0 msec 100.0 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Process latencytop (2798) Total: 486.0 msec
Waiting for event (poll) 4.0 msec 99.4 %
poll_schedule_timeout do_sys_poll sys_poll
system_call_fastpath
Waiting for a process to die 2.1 msec 0.6 %
do_wait sys_wait4 system_call_fastpath