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List:       linux1394-devel
Subject:    Re: [FFADO-devel] [PATCH 7/7] firewire: allow explicit flushing of iso packet completions
From:       Jonathan Woithe <jwoithe () just42 ! net>
Date:       2012-03-19 23:28:33
Message-ID: 20120319231633.GF4924 () marvin ! atrad ! com ! au
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Hi Clemens

> Does anybody know why FFADO's ISOHANDLER_FLUSH_BEFORE_ITERATE is
> disabled by default?
> (The comments of STREAMPROCESSORMANAGER_ALLOW_DELAYED_PERIOD_SIGNAL
> seem to indicate that some flushing would be useful, but I don't
> know if these are related.)

No, sorry, no idea.  I've never really delved into the streaming code to
that low a level.  I can only suggest possible reasons: for example, it may
have upset the old stack, or perhaps some firewire cards can't cope with the
effects.  However, these are all really just guesses.

> Okay, my tests show that this is called very soon after getting
> an interrupt from the fw stream, and so it hardly ever happens that
> there is some packet to flush, especially when using small period sizes.

Hmm, so it may be an early optimisation that was done but which proved
unnecessary or ineffective later on.  The comments associated with
STREAMPROCESSORMANAGER_ALLOW_DELAYED_PERIOD_SIGNAL may date from that
earlier time.

Regards
  jonathan

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