IO degradation in 2.4.17-pre2 vs. 2.4.16

[Jason Holmes]

I saw in a previous thread that the interactivity improvements in
2.4.17-pre2 had some adverse effect on IO throughput and since I was
already evaluating 2.4.16 for a somewhat large fileserving project, I
threw 2.4.17-pre2 on to see what has changed.  Throughput while serving
a large number of clients is important to me, so my tests have included
using dbench to try to see how things scale as clients increase.

2.4.16:

Throughput 116.098 MB/sec (NB=145.123 MB/sec  1160.98 MBit/sec)  1 procs
Throughput 206.604 MB/sec (NB=258.255 MB/sec  2066.04 MBit/sec)  2 procs
Throughput 210.364 MB/sec (NB=262.955 MB/sec  2103.64 MBit/sec)  4 procs
Throughput 213.397 MB/sec (NB=266.747 MB/sec  2133.97 MBit/sec)  8 procs
Throughput 210.989 MB/sec (NB=263.736 MB/sec  2109.89 MBit/sec)  16
procs
Throughput 138.713 MB/sec (NB=173.391 MB/sec  1387.13 MBit/sec)  32
procs
Throughput 117.729 MB/sec (NB=147.162 MB/sec  1177.29 MBit/sec)  64
procs
Throughput 66.7354 MB/sec (NB=83.4193 MB/sec  667.354 MBit/sec)  128
procs

2.4.17-pre2:

Throughput 96.2302 MB/sec (NB=120.288 MB/sec  962.302 MBit/sec)  1 procs
Throughput 226.679 MB/sec (NB=283.349 MB/sec  2266.79 MBit/sec)  2 procs
Throughput 223.955 MB/sec (NB=279.944 MB/sec  2239.55 MBit/sec)  4 procs
Throughput 224.533 MB/sec (NB=280.666 MB/sec  2245.33 MBit/sec)  8 procs
Throughput 153.672 MB/sec (NB=192.09 MB/sec  1536.72 MBit/sec)  16 procs
Throughput 91.3464 MB/sec (NB=114.183 MB/sec  913.464 MBit/sec)  32
procs
Throughput 64.876 MB/sec (NB=81.095 MB/sec  648.76 MBit/sec)  64 procs
Throughput 54.9774 MB/sec (NB=68.7217 MB/sec  549.774 MBit/sec)  128
procs

Throughput 136.522 MB/sec (NB=170.652 MB/sec  1365.22 MBit/sec)  1 procs
Throughput 223.682 MB/sec (NB=279.603 MB/sec  2236.82 MBit/sec)  2 procs
Throughput 222.806 MB/sec (NB=278.507 MB/sec  2228.06 MBit/sec)  4 procs
Throughput 224.427 MB/sec (NB=280.534 MB/sec  2244.27 MBit/sec)  8 procs
Throughput 152.286 MB/sec (NB=190.358 MB/sec  1522.86 MBit/sec)  16
procs
Throughput 92.044 MB/sec (NB=115.055 MB/sec  920.44 MBit/sec)  32 procs
Throughput 78.0881 MB/sec (NB=97.6101 MB/sec  780.881 MBit/sec)  64
procs
Throughput 66.1573 MB/sec (NB=82.6966 MB/sec  661.573 MBit/sec)  128
procs

Throughput 117.95 MB/sec (NB=147.438 MB/sec  1179.5 MBit/sec)  1 procs
Throughput 212.469 MB/sec (NB=265.586 MB/sec  2124.69 MBit/sec)  2 procs
Throughput 214.763 MB/sec (NB=268.453 MB/sec  2147.63 MBit/sec)  4 procs
Throughput 214.007 MB/sec (NB=267.509 MB/sec  2140.07 MBit/sec)  8 procs
Throughput 96.6572 MB/sec (NB=120.821 MB/sec  966.572 MBit/sec)  16
procs
Throughput 48.1342 MB/sec (NB=60.1677 MB/sec  481.342 MBit/sec)  32
procs
Throughput 71.3444 MB/sec (NB=89.1806 MB/sec  713.444 MBit/sec)  64
procs
Throughput 59.258 MB/sec (NB=74.0724 MB/sec  592.58 MBit/sec)  128 procs

I have included three runs for 2.4.17-pre2 to show how inconsistent its
results are; 2.4.16 didn't have this problem to this extent.  bonnie++
numbers seem largely unchanged between kernels, coming in around:

      ------Sequential Output------ --Sequential Input- --Random-
      -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
 Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
2512M 14348  81 49495  26 24438  16 16040  96 55006  15 373.7   1
      ------Sequential Create------ --------Random Create--------
      -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
   16  3087  99 +++++ +++ +++++ +++  3175 100 +++++ +++ 11042 100

The test machine is an IBM 342 with 2 1.26 GHz P3 processors and 1.25 GB
of RAM.  The above numbers were generated off of 1 10K RPM SCSI disk
hanging off of an Adaptec aix7899 controller.

--
Jason Holmes