Saturday, 3 July 2010

Dtrace progress .. restarted

After a long period not touching dtrace, I need to fix some things
in dtrace. Thanks to the people sending me bug reports or code

I fired up an Ubuntu 10.04 VirtualBox session - as I know theres something
erratic in this kernel causing dtrace to bomb out. I think I know
the culprit area - but need to drill down to find out what I am doing
wrong. (I recall a problem in using the cpu-calling functions which are
not interrupt level safe). A simple:

$ dtrace -n syscall:::

works for a bit and then generates kernel errors effectively crashing
the machine.

Also I need to fix the struct/typedef user level bug causing a strange
segmentation violation.

As an aside, I am temporarily pausing my research into full text indexing.
After reviewing my code, there are big bottlenecks in the way hash tables
are being manipulated - at exactly the areas I wasnt expecting - its not
the putting of words into the hash tables thats at fault but the
sorting the entries into alphabetical order on large hash tables
(300k+ entries) and allocating/clearing down these large hashes. I need
to do some fine tuning or look at better algorithms. Definitely interesting
that this should be the case.

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