From: Ken Bloom <kbloom@...>
Date: 2008-09-19T07:47:22+09:00
Subject: Re: Optimization help - reading out of /proc on Solaris

Brian Candler <b.candler@pobox.com> wrote:
>> Anyway, below is the code. I ran it through the profiler, but the top
>> two most costly ops were Dir.foreach, which I don't see any way to
>> optimize*, and the loop that gathers environment information, which I
>> again see no way to optimize.
> 
> Could you post your profiling? If you run using "time", how much user 
> CPU versus system CPU are you using?
> 
> Have you tried using Dir.open.each instead of Dir["/foo/*"]? Maybe 
> globbing is expensive.
> 
> Your environment loop does a fresh sysread(1024) for each var=val pair, 
> even if you've only consumed (say) 7 bytes from the previous call. You 
> would make many fewer system calls if you read a big chunk and chopped 
> it up afterwards. This may also avoid non-byte-aligned reads.
> 
> I would also be tempted to write one long unpack instead of lots of 
> string slicing and unpacking. The overhead here may be negligible, but 
> the code may end up being smaller and simpler. e.g.

Method calls are expensive. Right now he's got 3 per field (array
indexing, unpack, and assignment). He could get that down to 1 per
field (assignment only) pretty easily by following your suggestion.

-- 
Chanoch (Ken) Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu/~kbloom1/