[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] SCHED_FIFO and NPTL

From: Frank Brickle
Subject: Re: [Discuss-gnuradio] SCHED_FIFO and NPTL
Date: Wed, 08 Mar 2006 09:46:54 -0500
User-agent: Mozilla Thunderbird 1.0.6 (Windows/20050716)

Eric Blossom wrote:

Bottom line, it hasn't actually been proved that running SCHED_FIFO will squash the existing latency and continuity problems, so I'm not at all sure much is missing without that capability.

Frank, is this a statement or a question?

It's a statement. I don't have any real proof at the moment but I suspect SCHED_FIFO is a bit of a red herring. I haven't got proof because the couple of times I tried to actually measure a difference I tripped over additional activity that needed to be accounted for, like, for example, periodic journaling filesystem updates.

The other unfortunate consequence was that some kinds of X action on the desktop, like switching between multiple desktops, would get deferred -- it got real sluggish -- and then all the display activity would happen in a burst. Sometimes that would choke the audio worse than an occasional xrun. Oh, and the interaction with audio subsystem buffer sizes was unpredictable.

I'm suggesting that the current non-RT scheduling is very delicately balanced and there's no single, universal fix. What's more, I conjecture that the worst culprit is disk activity, specifically paging, and that the cost/benefit fix for that is running off ramdisk :-)

It would be *wonderful* to be wrong about this. As I said, it's just a strong hunch.

I'm not sure if the JACK FAQ is up to date or not.

Usually not :-)

Do you have data
on the success or failure of folks running JACK on ALSA using NPTL and
if they are able to get sufficiently good performance?  I guess Ardour
users would be a good test case.  How about the dttsp stuff under Linux?

Again, it ain't conclusive, but it looks like xruns are not a problem with DttSP under Linux. You're absolutely right, Ardour users are the ones to ask. I finally have it installed here and can check it out first hand, at long last.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]