I've started testing the 3.10 kernel, previously I was on 3.4, and I'm
encounting some fairly large stalls in my memory mapped writes in the
range of .01 to 1s. I've managed to capture two of these stalls so
far and both looked like the following:
1) Writing process writes to a new page and blocks on xfs_ilock:
<...>-21567 [009] 9435.453069: sched_switch: prev_comm=tick_receiver_m prev_pid=21567 prev_prio=79 prev_state=D ==> next_comm=swapper/9 next_pid=0 next_prio=120
<...>-21567 [009] 9435.453072: kernel_stack: <stack trace>
=> schedule (ffffffff814ca379)
=> rwsem_down_write_failed (ffffffff814cb095)
=> call_rwsem_down_write_failed (ffffffff81275053)
=> xfs_ilock (ffffffff8120b25c)
=> xfs_vn_update_time (ffffffff811cf3d3)
=> update_time (ffffffff81158dd3)
=> file_update_time (ffffffff81158f0c)
=> block_page_mkwrite (ffffffff81171d23)
=> xfs_vm_page_mkwrite (ffffffff811c5375)
=> do_wp_page (ffffffff8110c27f)
=> handle_pte_fault (ffffffff8110dd24)
=> handle_mm_fault (ffffffff8110f430)
=> __do_page_fault (ffffffff814cef72)
=> do_page_fault (ffffffff814cf2e7)
=> page_fault (ffffffff814cbab2)
2) kworker calls xfs_iunlock and wakes up my process:
kworker/u50:1-403 [013] 9436.027354: sched_wakeup: comm=tick_receiver_m pid=21567 prio=79 success=1 target_cpu=009
kworker/u50:1-403 [013] 9436.027359: kernel_stack: <stack trace>
=> ttwu_do_activate.constprop.34 (ffffffff8106c556)
=> try_to_wake_up (ffffffff8106e996)
=> wake_up_process (ffffffff8106ea87)
=> __rwsem_do_wake (ffffffff8126e531)
=> rwsem_wake (ffffffff8126e62a)
=> call_rwsem_wake (ffffffff81275077)
=> xfs_iunlock (ffffffff8120b55c)
=> xfs_iomap_write_allocate (ffffffff811ce4e7)
=> xfs_map_blocks (ffffffff811bf145)
=> xfs_vm_writepage (ffffffff811bfbc2)
=> __writepage (ffffffff810f14e7)
=> write_cache_pages (ffffffff810f189e)
=> generic_writepages (ffffffff810f1b3a)
=> xfs_vm_writepages (ffffffff811bef8d)
=> do_writepages (ffffffff810f3380)
=> __writeback_single_inode (ffffffff81166ae5)
=> writeback_sb_inodes (ffffffff81167d4d)
=> __writeback_inodes_wb (ffffffff8116800e)
=> wb_writeback (ffffffff811682bb)
=> wb_check_old_data_flush (ffffffff811683ff)
=> wb_do_writeback (ffffffff81169bd1)
=> bdi_writeback_workfn (ffffffff81169cca)
=> process_one_work (ffffffff81059104)
=> worker_thread (ffffffff8105a1bc)
=> kthread (ffffffff810605f0)
=> ret_from_fork (ffffffff814d395c)
In this case my process stalled for roughly half a second:
<...>-21567 [009] 9436.027388: print: tracing_mark_write: stall of 0.574282
So I guess my question is does anyone know why I'm now seeing these
stalls with 3.10? Are there any suggestions for how to eliminate them?
# xfs_info /home/
meta-data=/dev/sda5 isize=256 agcount=4, agsize=67774016 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=271096064, imaxpct=5
= sunit=0 swidth=0 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal bsize=4096 blocks=132371, version=2
= sectsz=512 sunit=0 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
# grep sda5 /proc/mounts
/dev/sda5 /home xfs rw,noatime,nodiratime,attr2,nobarrier,inode64,noquota 0 0
Thanks,
Shawn
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