I tried using cp to copy the linux git tree between
pmem devices like this:
cp -r /mnt/xfs-pmem1/linux /mnt/xfs-pmem2
The time taken by various filesystems varies (4.4-rc5):
* xfs w/dax: 42 s
* xfs no dax: 14 s
* ext4 w/dax: 7 s
* ext4 no dax: 15 s
* btrfs no dax: 18 s
mount options:
* /dev/pmem1 on /mnt/xfs-pmem1 type xfs (rw,relatime,seclabel,attr2,dax,inode64,noquota)
* /dev/pmem1 on /mnt/ext4-pmem1 type ext4 (rw,relatime,seclabel,dax,data=ordered)
* /dev/pmem1 on /mnt/btrfs-pmem1 type btrfs (rw,relatime,seclabel,ssd,space_cache,subvolid=5,subvol=/)
xfs with dax spends most of the time in clear_page_c_e and
dax-clear_blocks (from "perf top"):
30.06% [kernel] [k] clear_page_c_e
12.24% [kernel] [k] dax_clear_blocks
5.36% [kernel] [k] copy_user_enhanced_fast_string
4.33% [kernel] [k] __copy_user_nocache
2.55% [xfs] [k] xfs_perag_put
1.77% [kernel] [k] security_compute_sid.part.12
1.19% [kernel] [k] __percpu_counter_sum
1.14% [kernel] [k] acpi_os_write_port
1.03% [kernel] [k] dax_do_io
1.00% [kernel] [k] _raw_spin_lock
The others spend most of their time in the
copy_user_enhanced_fast_string and __copy_user_nocache
functions that actually copy data.
xfs without dax:
28.82% [kernel] [k] copy_user_enhanced_fast_string
7.48% [kernel] [k] __copy_user_nocache
3.63% [kernel] [k] __block_commit_write.isra.22
1.86% [kernel] [k] acpi_os_write_port
1.72% [kernel] [k] filenametr_cmp
1.48% [kernel] [k] hashtab_search
1.28% [kernel] [k] security_compute_sid.part.12
0.96% [kernel] [k] _raw_spin_lock
ext4 with dax:
22.85% [kernel] [k] __copy_user_nocache
22.51% [kernel] [k] copy_user_enhanced_fast_string
4.15% [kernel] [k] mb_find_order_for_block
3.03% [kernel] [k] dax_do_io
2.08% [kernel] [k] __d_lookup_rcu
1.85% [kernel] [k] mb_find_extent
1.75% [kernel] [k] ext4_mark_iloc_dirty
1.54% [kernel] [k] acpi_os_write_port
1.15% [kernel] [k] _find_next_bit.part.0
0.99% [kernel] [k] ext4_mb_good_group
ext4 without dax:
29.89% [kernel] [k] copy_user_enhanced_fast_string
15.81% [kernel] [k] __copy_user_nocache
4.45% [kernel] [k] __block_commit_write.isra.22
1.39% [kernel] [k] ext4_mark_iloc_dirty
1.37% [kernel] [k] ext4_bio_write_page
1.12% [kernel] [k] filenametr_cmp
1.09% [kernel] [k] security_compute_sid.part.12
0.98% [kernel] [k] hashtab_search
btrfs (without dax):
14.25% [kernel] [k] copy_user_enhanced_fast_string
14.12% [kernel] [k] queued_spin_lock_slowpath
9.70% [kernel] [k] __copy_user_nocache
3.48% [kernel] [k] acpi_os_write_port
1.52% [kernel] [k] _raw_spin_lock
1.38% [kernel] [k] queued_write_lock_slowpath
1.36% [kernel] [k] _raw_spin_lock_irqsave
---
Robert Elliott, HPE Persistent Memory
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
