Re: Linux Kernel Markers - performance characterization with large IO load on large-ish system

["Alan D. Brunelle" <Alan.Brunelle@hp.com>]

Taking Linux 2.6.23-rc6 + 2.6.23-rc6-mm1 as a basis, I took some sample 
runs of the following on both it and after applying Mathieu Desnoyers 
11-patch sequence (19 September 2007).

   * 32-way IA64 + 132GiB + 10 FC adapters + 10 HP MSA 1000s (one 72GiB
     volume per MSA used)

   * 10 runs with each configuration, averages shown below
         o 2.6.23-rc6 + 2.6.23-rc6-mm1 without blktrace running
         o 2.6.23-rc6 + 2.6.23-rc6-mm1 with blktrace running
         o 2.6.23-rc6 + 2.6.23-rc6-mm1 + markers without blktrace running
         o 2.6.23-rc6 + 2.6.23-rc6-mm1 + markers with blktrace running

   * A run consists of doing the following in parallel:
         o Make an ext3 FS on each of the 10 volumes
         o Mount & unmount each volume
               + The unmounting generates a tremendous amount of writes
                 to the disks - thus stressing the intended storage
                 devices (10 volumes) plus the separate volume for all
                 the blktrace data (when blk tracing is enabled).
               + Note the times reported below only cover the
                 make/mount/unmount time - the actual blktrace runs
                 extended beyond the times measured (took quite a while
                 for the blk trace data to be output). We're only
                 concerned with the impact on the "application"
                 performance in this instance.

Results are:

Kernel                                 w/out BT   STDDEV     w/ BT    STDDEV
-------------------------------------  ---------  ------   ---------  ------
2.6.23-rc6 + 2.6.23-rc6-mm1            14.679982    0.34   27.754796    2.09
2.6.23-rc6 + 2.6.23-rc6-mm1 + markers  14.993041    0.59   26.694993    3.23

It looks to be about 2.1% increase in time to do the make/mount/unmount 
operations with the marker patches in place and no blktrace operations. 
With the blktrace operations in place we see about a 3.8% decrease in 
time to do the same ops.

When our Oracle benchmarking machine frees up, and when the 
marker/blktrace patches are more stable, we'll try to get some "real" 
Oracle benchmark runs done to gage the impact of the markers changes to 
performance...

Alan D. Brunelle
Hewlett-Packard / Open Source and Linux Organization / Scalability and 
Performance Group

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