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From: Lutz Donnerhacke <lutz@iks-jena.de>
Newsgroups: comp.lang.ada
Subject: High CPU in tasking
Date: Thu, 24 Jun 2004 15:43:46 +0000 (UTC)
Organization: IKS GmbH Jena
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Date: 2004-06-24T15:43:46+00:00
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In order to stop others falling into the same mistake, I debugged several
days.

I wrote an data stream decoder and output (via TCP) manifolder using Ada
tasking and a protected ringbuffer. The whole application word fine, but the
CPU load increased linear on input load and dramatically over the number of
output queues.

Debugging turned out:
  - Every writing to the ringbuffer wakes up all reader tasks.
  - That's why the reader buffers were filled with only the little data amount
    just written.
  - Tasking overhead caused the CPU load.

Two solutions (used both):
  - The ringbuffer got a minimum reading length => Fewer wakeups.
  - The writer task collect a lot of data before writing
    => Fewer checks for wakeup.

The ratio of tasking events before and after the change is about 30:1.

Conclusion:
  When implementing tasking synchonisation with protected objects,
  keep in mind, that the standard Ada tasking model generates a near real
  time experience, which is mostly not required.

HTH