Re: [PATCH 2/7] locking/rwsem: more aggressive use of optimistic spinning

From: Waiman Long
Date: Fri Aug 15 2014 - 13:58:18 EST

On 08/14/2014 11:34 PM, Dave Chinner wrote:

<create sparse vm image file of 500TB on ssd with XFS on it>
xfs_io -f -c "truncate 500t" -c "extsize 1m" /path/to/vm/image/file

<start 16p/16GB RAM vm with image file configured as:
-drive file=/path/to/vm/image/file,if=virtio,cache=none>

In vm:

download and build fsmark from here:


download and install xfsprogs v3.2.1 from here:

git:// tags/v3.2.1

Setup up the target filesystem:

# mkfs.xfs -f -m "crc=1,finobt=1" /dev/vda
# mount -o logbsize=262144,nobarrier /dev/vda /mnt/scratch


# fs_mark -D 10000 -S0 -n 50000 -s 0 -L 32 \
-d /mnt/scratch/0 -d /mnt/scratch/1 \
-d /mnt/scratch/2 -d /mnt/scratch/3 \
-d /mnt/scratch/4 -d /mnt/scratch/5 \
-d /mnt/scratch/6 -d /mnt/scratch/7 \
-d /mnt/scratch/8 -d /mnt/scratch/9 \
-d /mnt/scratch/10 -d /mnt/scratch/11 \
-d /mnt/scratch/12 -d /mnt/scratch/13 \
-d /mnt/scratch/14 -d /mnt/scratch/15 \

If you've got everything set up right, that should run at around
200-250,000 file creates/s. When finished, unmount and run:

# xfs_repair -o bhash=500000 /dev/vda

And that should spend quite a long while pounding on the mmap_sem
until the the userspace buffer cache stops growing.

I just ran the above on 3.16, saw this from perf:

37.30% [kernel] [k] _raw_spin_unlock_irqrestore
- _raw_spin_unlock_irqrestore
- 62.00% rwsem_wake
- call_rwsem_wake
+ 83.52% sys_mprotect
+ 16.23% __do_page_fault
+ 35.15% try_to_wake_up
+ 0.96% update_blocked_averages
+ 0.61% pagevec_lru_move_fn
- 23.35% [kernel] [k] _raw_spin_unlock_irq
- _raw_spin_unlock_irq
+ 51.37% finish_task_switch
+ 39.37% rwsem_down_write_failed
+ 8.49% rwsem_down_read_failed
0.62% run_timer_softirq
+ 5.22% [kernel] [k] native_read_tsc
+ 3.89% [kernel] [k] rwsem_down_write_failed



Thank for the testing recipe. I am afraid that I can't find a 500TB SSD for testing purpose. Do you think the test will still be valid for exercising rwsem if I use a smaller SSD or maybe mechanical hard disk?

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