Christoph Hellwig <hch@lst.de> writes:

> Snipping the long contest:
>
> I think there are three observations here:
>
>  (1) removing the mark_page_accessed (which is the only significant
>      change in the parent commit)  hurts the
>      aim7/1BRD_48G-xfs-disk_rr-3000-performance/ivb44 test.
>      I'd still rather stick to the filemap version and let the
>      VM people sort it out.  How do the numbers for this test
>      look for XFS vs say ext4 and btrfs?
>  (2) lots of additional spinlock contention in the new case.  A quick
>      check shows that I fat-fingered my rewrite so that we do
>      the xfs_inode_set_eofblocks_tag call now for the pure lookup
>      case, and pretty much all new cycles come from that.
>  (3) Boy, are those xfs_inode_set_eofblocks_tag calls expensive, and
>      we're already doing way to many even without my little bug above.
>
> So I've force pushed a new version of the iomap-fixes branch with
> (2) fixed, and also a little patch to xfs_inode_set_eofblocks_tag a
> lot less expensive slotted in before that.  Would be good to see
> the numbers with that.

For the original reported regression, the test result is as follow,

=========================================================================================
compiler/cpufreq_governor/debug-setup/disk/fs/kconfig/load/rootfs/tbox_group/test/testcase:
  gcc-6/performance/profile/1BRD_48G/xfs/x86_64-rhel/3000/debian-x86_64-2015-02-07.cgz/ivb44/disk_wrt/aim7

commit: 
  f0c6bcba74ac51cb77aadb33ad35cb2dc1ad1506 (parent of first bad commit)
  68a9f5e7007c1afa2cf6830b690a90d0187c0684 (first bad commit)
  99091700659f4df965e138b38b4fa26a29b7eade (base of your fixes branch)
  bf4dc6e4ecc2a3d042029319bc8cd4204c185610 (head of your fixes branch)

f0c6bcba74ac51cb 68a9f5e7007c1afa2cf6830b69 99091700659f4df965e138b38b bf4dc6e4ecc2a3d042029319bc 
---------------- -------------------------- -------------------------- -------------------------- 
         %stddev     %change         %stddev     %change         %stddev     %change         %stddev
             \          |                \          |                \          |                \  
    484435 ±  0%     -13.3%     420004 ±  0%     -17.0%     402250 ±  0%     -15.6%     408998 ±  0%  aim7.jobs-per-min


And the perf data is as follow,

  "perf-profile.func.cycles-pp.intel_idle": 20.25,
  "perf-profile.func.cycles-pp.memset_erms": 11.72,
  "perf-profile.func.cycles-pp.copy_user_enhanced_fast_string": 8.37,
  "perf-profile.func.cycles-pp.__block_commit_write.isra.21": 3.49,
  "perf-profile.func.cycles-pp.block_write_end": 1.77,
  "perf-profile.func.cycles-pp.native_queued_spin_lock_slowpath": 1.63,
  "perf-profile.func.cycles-pp.unlock_page": 1.58,
  "perf-profile.func.cycles-pp.___might_sleep": 1.56,
  "perf-profile.func.cycles-pp.__block_write_begin_int": 1.33,
  "perf-profile.func.cycles-pp.iov_iter_copy_from_user_atomic": 1.23,
  "perf-profile.func.cycles-pp.up_write": 1.21,
  "perf-profile.func.cycles-pp.__mark_inode_dirty": 1.18,
  "perf-profile.func.cycles-pp.down_write": 1.06,
  "perf-profile.func.cycles-pp.mark_buffer_dirty": 0.94,
  "perf-profile.func.cycles-pp.generic_write_end": 0.92,
  "perf-profile.func.cycles-pp.__radix_tree_lookup": 0.91,
  "perf-profile.func.cycles-pp._raw_spin_lock": 0.81,
  "perf-profile.func.cycles-pp.entry_SYSCALL_64_fastpath": 0.79,
  "perf-profile.func.cycles-pp.__might_sleep": 0.79,
  "perf-profile.func.cycles-pp.xfs_file_iomap_begin_delay.isra.9": 0.7,
  "perf-profile.func.cycles-pp.__list_del_entry": 0.7,
  "perf-profile.func.cycles-pp.vfs_write": 0.69,
  "perf-profile.func.cycles-pp.drop_buffers": 0.68,
  "perf-profile.func.cycles-pp.xfs_file_write_iter": 0.67,
  "perf-profile.func.cycles-pp.rwsem_spin_on_owner": 0.67,

Best Regards,
Huang, Ying