Re: Scatter Gather and odd period sizes.

[Takashi Iwai <tiwai@suse.de>]

At Mon, 17 Mar 2003 16:12:24 -0400,
mjander wrote:
> 
> hi,
> 
> >
> >i'm not sure how the aureal driver works.  IIRC, it can use up to 4 x
> >4k pages, right?  if its size is really only 4 pages, i'd
> recommend to
> >use a simple phyically linear buffer.
> >
> >
> >Takashi
> >
> 
> In the meanwhile i managed to use SG buffer by simply setting the
> period max and minimal size to 0x1000 (4KiB). I even implemented a
> page extender, such like the CSxxx patch  that extends 2 physical
> (4 in this case) periods into unlimited periods, but i couldn't
> measure any improvement (less skipping on high  load  or the
> like). So i think i better stay with linear buffers, and map the
> physical pages in a linear  fashion.
> Using this approach the buffer size extender mechanism for more
> periods is still  possible.

yes.

> What I still don't understand, after my experiments: Why should i
> use Scatter Gather ? As far as  i  can tell, it doesnt provide any
> advantage, except that you can use smaller chunks of memory when
> larger ones arent avaiable.

correct.  the only advantage is the memory usage.


> Someone talked about "the  faster
> Scatter Gather"...
> Why "faster"?

most likely it's a misunderstanding.

for the hardware, it won't make difference regarding the speed (except
for very tiny issues like cache, etc :)
for the driver, as you noticed, it will even increase the work you
need to do.



ciao,

Takashi


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