gbde performance question

[Heiko Schaefer]

Hey all, especially Poul,

putting my hardware troubles (still working on those, i am planning to buy
intel-based, non-el-cheapo hardware tomorrow, if i can get any more
flipped bits unti then. i've exhausted all possible causes that i care to
check, by now) aside for a minute, i wanted to ask about the performance i
see.

to be blunt, i wonder what is taking gbde so long to do its thing :)
less bluntly, i'm looking for input if i am interpreting the numbers i see
correctly, and if they make sense to someone who knows the code.

my hardware (again) is a amd athlon xp+ 1800, i got 512mb of ddr ram.

what i do is that i copy data between two local gbde encrypted disks (two
separate, rather modern - udma 66/100 - disks, on two different
controllers).

iostat 1 says something like that:

      tty             ad0              ad1              ad2             cpu
tin tout  KB/t tps  MB/s   KB/t tps  MB/s   KB/t tps  MB/s  us ni sy in id
  0  153 60.57 139  8.25   0.00   0  0.00  31.37 285  8.73   0  0 89  2  9
  0  152 60.52 136  8.06   0.00   0  0.00  31.39 284  8.72   0  0 91  0  9
  0  153 60.28 144  8.45   0.00   0  0.00  31.15 294  8.95   0  0 92  2  6
  0  153 58.17 143  8.11   0.00   0  0.00  31.35 282  8.62   0  0 88  2  9


i get roughtly 9 MB/s throughput on each disk (one disk writing, one
reading) - and most of the time iostat (just like top) says that my cpu is
more or less saturated.

in "ps auwx" i see

USER    PID %CPU %MEM   VSZ  RSS  TT  STAT STARTED      TIME COMMAND
root    509 37.9  0.0     0   12  ??  DL    9:53AM  22:24.24  (g_bde ad2s1e.bde)
root    513 34.3  0.0     0   12  ??  DL    9:53AM  11:49.08  (g_bde ad0s1e.bde)

i figure this is the amount of cpu time that is used by raw number
crunching (and for example does not include disk-io or anything of that
sort). that would mean that ~1/3 of my cpu can do ~8 MB/s of gbde's
crypto. if so, i could estimate that gbde can theoretically process
roughly 25MB/s on this athlon 1800+.

that looks like an rather low number to me. sites such as

http://www.tcs.hut.fi/~helger/aes/rijndael.html

suggest that on a cpu of that speed, memory bandwidth should be the
limiting factor when using AES/Rijndael.

am i overlooking something ?!


thanks for any insight you can provide on the matter, regards,

Heiko

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