Re: async-io

----- Original Message -----
From: Henrik Nordstrom <hno@hem.passagen.se>
To: Adrian Chadd <adrian@creative.net.au>
Cc: <squid-dev@squid-cache.org>
Sent: Sunday, April 23, 2000 8:05 PM
Subject: Re: async-io

> Adrian Chadd wrote:
>
> > I meant a queue of operations which is maintained linearly. Then you
> > can look at implementing elevator sorts and simple
clustering/prefetching
> > where applicable. I don't want to have too much magic in the aiops
> > code, but enough to prevent replication of code.
>
> It is a single linear FIFO queue where all unstarted operations live
> until the async-io request sheduler assigns them to a worker thread one
> request per thread at a time.
>
> For the UFS store there isn't much clustering or elevator sorting to
> perform as there only are one outstanding request per fd at a time.. For
> COSS it might be an idea to elevator sort reads, but I am not sure the
> benefit is that high from it. There are a lot simpler optimizations from
> which I expect a lot more to be gained.

Just a quick note.

I think that elevator sorting really could be a big benefit. I did some
quick benchmarking about a month ago..wrote a quick program that just
randomly seeks/reads x many times around the disk, and times the results. I
got about 30 ops/second. Then, I generated a list of those requests, sorted
them, and ran them through and ended up with about 60 ops/second. My
conclusions were:
1) sorting (ie reducing seek distance) is a HUGE benefit
2) HD's are MUCH slower than my instincts indicated

Eric Stern - Senior Product Developer - Industrial Code & Logic Inc. - (519)
249-0508
http://www.indcl.com http://www.cachexpress.com
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Received on Mon Apr 24 2000 - 11:55:15 MDT