Re: High CPU in tasking

[Lutz Donnerhacke <lutz@iks-jena.de>]

* Nick Roberts wrote:
> "Lutz Donnerhacke" <lutz@iks-jena.de> wrote in message
>> > Do you not have a separate buffer for each reader (of a single
>> > demultiplexed stream)?
>>
>> Yep. I do have a ringbuffer with a single "writer" and an indetermined
>> number of "readers". The data structure is a protected type with an entry
>> family for all readers.
>
> Would it be possible to have a separate protected object container a buffer
> for each reader?

In this case, the writer has to fill an unconstraint array of ringbuffers.
This seems much more inefficient.

> The idea is that the writer task: accepts a data packet; determines which
> reader it belongs to;

Every data belongs to every reader. It's a manifolder which clones the whole
data to many receivers.

> If this approach is possible, I think it might more neatly solve your
> problem ...

The problem is solved. I published my solution to point others to this
pitfall.

>> All the same. I'm currently testing with a data source of 1GB/h and eight
>> data sources of about half the rate. Each data source allocates a
>> ringbuffer.
>
> ... especially if you make the writer a higher priority than all the
> readers.

Why? This would cause the writer to overwrite the ringbuffer without any
reading access.

>> There are controlling tasks: A logger task writing to /dev/log, because
>> syslog(3) is not thread safe, and a supervisor task for handling the
>> commands on each the TCP session.
>
> I suggest the logger task should made a lower priority than all the other
> tasks (so that it tends to work in the gaps between reader and writer
> activity). I suggest the supervisor task be made a higher priority than all
> the other tasks, so as to minimise any delay in acting on incoming commands
> (such as 'stop' ;-)

The whole program is event triggered. There are no free running code
sequences. The only effect I can imagine will be a deadlock ;-)