Subject: Re: [linux-audio-dev] Re: Low Latency Kernel Combos
From: Josh Green (jgreen_AT_users.sourceforge.net)
Date: Thu Jun 21 2001 - 15:02:19 EEST
Benno Senoner wrote:
>
> Notice that the output of latencytest is stereo thus a framentsize of 128byte
> means 32 samples/fragment (32 * 16bit * 2 channels = 128bytes)
>
> each fragment has a latency of 0.7msec therefore 3 x 0.7 = 2.1msec latency.
>
> Josh, although your tests look very good, it seems that the soundcard uses
> only 2 fragments rather than 3. (that would mean that the effective latency
> would be 1.4msec :-) )
>
> The strange thing on your tests is that in the 3 x 256 test you posted,
> 3 fragments get allocated. (see the red line).
>
> If the test with fragsize=256 used 2 fragments too, then I'd say that your
> card is setting wrong fragsizes all the time but in your case it seems that
> it's ok for 3x256 but not for 3x128.
>
Ohh. I wouldn't be surprised actually if I ran the first test with OSS
and the second with ALSA. Which kind of breaks my comparison and might
account for the very nice performance in the second test (ALSA). Perhaps
an OSS versus ALSA comparison would be cool :) I'll be sure to update
those tests with more thorough information.
>
> Josh: regarding the latencytest database:
> I was thinking about the following: use the phpnuke engine, make a topic
> "low latency" and then users can simply submit their results.
> That way people interested in low latency simply click to the lowlatency icon
> and see all latest news on the matter (new tests like yours, new patches, rpms
> etc).
> Would this be ok folks ?
>
Yes, I think a place to discuss and announce Linux latency related stuff
would be cool. But I also think a good database of results would also be
nice and helpful as Linux low latency becomes more widely desired :)
Such a database could have fields for types of hardware, kernel version,
patches, user notes and information on the latency results for different
fragment/buffer size combinations. I seem to remember talking about this
before. I think it would be very helpful though for those planning on
buying specific hardware for Linux low latency, trying to figure out
what particular hardware is causing problems, etc. You could search/sort
by various fields.. blah.
Anyone have any thoughts on how useful something like this might be? I
think I will start coding one now :) A fine time to get interested in
another project (5am where I am, haven't gone to sleep yet). Josh
Green
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