On 6/26/12 4:44 PM, Eric Sandeen wrote:

On 6/26/12 3:57 PM, Eric Sandeen wrote:

quoted

On 6/26/12 3:30 PM, Ric Wheeler wrote:

...

quoted

I tried running this fio recipe on v3.3, which I think does a decent job of
emulating the situation (fallocate 1G, do random 1M writes into it, with
fsyncs after each):

[test]
filename=testfile
rw=randwrite
size=1g
filesize=1g
bs=1024k
ioengine=sync
fallocate=1
fsync=1

I realized the kernel I tested on had a lot of debugging bells & whistles turned on.  For a more performance-configured v3.3 kernel, I see much less impact, more or less negligible:

unwritten conversion on ext4:

  WRITE: io=1024.0MB, aggrb=23077KB/s, minb=23631KB/s, maxb=23631KB/s, mint=45437msec, maxt=45437msec
  WRITE: io=1024.0MB, aggrb=23040KB/s, minb=23593KB/s, maxb=23593KB/s, mint=45511msec, maxt=45511msec
  WRITE: io=1024.0MB, aggrb=23011KB/s, minb=23564KB/s, maxb=23564KB/s, mint=45567msec, maxt=45567msec

overwrites on ext4:

  WRITE: io=1024.0MB, aggrb=23046KB/s, minb=23599KB/s, maxb=23599KB/s, mint=45499msec, maxt=45499msec
  WRITE: io=1024.0MB, aggrb=23222KB/s, minb=23780KB/s, maxb=23780KB/s, mint=45153msec, maxt=45153msec
  WRITE: io=1024.0MB, aggrb=23031KB/s, minb=23584KB/s, maxb=23584KB/s, mint=45528msec, maxt=45528msec


So I guess it's interesting information; the debug kernel showed a much bigger difference; the performance-config'd kernel showed almost no difference.

FWIW, on this same kernel,

unwritten conversion on xfs:

  WRITE: io=1024.0MB, aggrb=28409KB/s, minb=29091KB/s, maxb=29091KB/s, mint=36909msec, maxt=36909msec
  WRITE: io=1024.0MB, aggrb=28372KB/s, minb=29053KB/s, maxb=29053KB/s, mint=36958msec, maxt=36958msec
  WRITE: io=1024.0MB, aggrb=28406KB/s, minb=29088KB/s, maxb=29088KB/s, mint=36913msec, maxt=36913msec

overwrites on xfs:

  WRITE: io=1024.0MB, aggrb=28268KB/s, minb=28946KB/s, maxb=28946KB/s, mint=37094msec, maxt=37094msec
  WRITE: io=1024.0MB, aggrb=28316KB/s, minb=28995KB/s, maxb=28995KB/s, mint=37031msec, maxt=37031msec
  WRITE: io=1024.0MB, aggrb=28576KB/s, minb=29262KB/s, maxb=29262KB/s, mint=36694msec, maxt=36694msec

-Eric