On 07/25/2012 04:20 AM, Christoph Hellwig wrote:
> On Wed, Jul 25, 2012 at 08:31:10AM +1000, Dave Chinner wrote:
>> FWIW, if you are going to change generic code, you need to present
>> results for other filesystems as well (xfs, btrfs are typical), as
>> they may not have the same problems as ext4 or react the same way to
>> your change. The result might simply be "it is 20% slower"....
> 
> And most importantly block devices, as they are one of the biggest
> use cases of AIO.  With an almost no-op get_blocks callback I can't
> see how this change would provide any gain there.

I tried running fio against a block device, disk partition and a
ramdisk. I ran this with a single job though. For disks, bandwidth
seems to stay nearly the same with submit latencies getting better.
And for ramdisk, bandwidth also sees improvement. I should probably
be doing better tests, any suggestions on what or how I can test?
For block devices, if the patch doesn't make it worse, at least, then
that should be good enough?

------ disk -------
                                      submit latencies(usec)
       	B/w       iops   runtime     min  max   avg  std dev
Read :
Old:  417335 B/s  101   252668msec     4  231  40.03  21.66
New:  419099 B/s  102   251282msec     0  169   8.20   6.95

Write:
Old:  412667 B/s  100   252668msec     3  272  47.65  24.58
New:  415481 B/s  101   251282msec     0  134   7.95   7.11

------ ramdisk -------
                                      submit latencies(usec)
       	B/w       iops      runtime   min  max   avg  std dev
Read:
Old:  708235KB/s  177058   1227msec     1   51   1.61  0.72
New:  822157KB/s  205539   1059msec     0   14   0.38  0.52

Write:
Old:  710510KB/s  177627   1227msec     2   46   2.33  0.81
New:  821658KB/s  205414   1059msec     0   24   0.40  0.53

Full fio results are attached, and I dropped cache before running
the tests.

-- 
Ankit Jain
SUSE Labs