Re: Re: dmix plugin

[Abramo Bagnara <abramo.bagnara@libero.it>]

Jaroslav Kysela wrote:
> 
> On Mon, 17 Feb 2003, Jaroslaw Sobierski wrote:
> 
> > >> I see, the read/saturate/write must be atomic, too. In this case, it would
> > >> be better to use a global (or a set of) mutex(es) to lock the hardware
> > >> ring buffer. The futexes are nice.
> > >
> > >They are nice indeed, but definitely not the right solution here.
> > >
> > >Although I don't know if it's the absolute best solution, the 'retry'
> > >approach I've proposed is far better and much more efficient.
> >
> > I have to agree with Abramo. A global mutex would cause long and unnecessary
> > waits for the processes trying to write to the plugin. Locking access to
> > individual parts of the buffer is messy. Notice that concurrent writes
> > to the same sample in the buffer will occur sporadically, and the "re-read"
> > in the loop costs almost nothing, while synchronization mechanisms could
> > block often.
> 
> Note that your all nice ideas go to some blind alley. Who will silence the
> sum buffer? Driver silences only hardware buffer which will not be used
> for the calculation in your algorithm.


Not so blind ;-)

	v = *src;
	if (cmpxchg(hw, 0, 1) == 0)
		v -= *sw;
        xadd(sw, v);
        do {
                v = *sw;
                if (v > 0x7fff)
                        s = 0x7fff;
                else if (v < -0x8000)
                        s = -0x8000;
                else
                        s = v;
                *hw = s;
        } while (unlikely(v != *sw));

I've convinced you?

However as I've written in the my first message the evil of dmix
approach lies in details: they might destroy efficiency of approach
rather easily.

-- 
Abramo Bagnara                       mailto:abramo.bagnara@libero.it

Opera Unica                          Phone: +39.546.656023
Via Emilia Interna, 140
48014 Castel Bolognese (RA) - Italy


-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf