disk encryption performance hit

[Jeff Bastian]

What kind of performance hit should full disk encryption entail?

I installed F9 yesterday under VMware Fusion 1.1.2 and enabled disk 
encryption.  It was working fine until cron fired up makewhatis.  At that 
point the system became so sluggish it was basically unusable.  Mouse 
clicks would sometimes work, sometimes get ignored, and some key strokes 
would get ignored, others would get doubled (i.e., typing 'foo' might end 
up with 'ffo' on the screen).

According to 'top', makewhatis was consuming the most CPU, but only about 
4%, followed by kcryptd.  However, the CPU was spending 85%+ on system 
tasks.

I noticed it was taking a long time to run makewhatis, so I ran 'time 
/etc/cron.weekly/makewhatis.cron' to see just how long and got:
    real    34m44.606s
    user    3m18.520s
    sys     13m46.823s

I switched back to my Fedora 8 virtual machine (same host) and repeated 
the test and got:
    real    7m1.667s
    user    2m45.410s
    sys     3m4.970s


That's quite a performance hit for disk encryption...  Is there something 
I can tune to speed this up?  Or maybe I should just encrypt /home instead 
of the whole disk.

FWIW, I have VMI enabled in VMware Fusion, and I'm booting with kernel 
command line args
    elevator=noop clocksource=vmi-timer
on both systems.

Jeff