Stereo Tool

Hello,

I am running 7.71 (released version) 64bit on Ubuntu 15.10. Running in realtime (lowlatency kernel) at a prio of 83 (soundcard at 95, jackd at 89).

My host is a i5 Macbook Pro. I am testing with a built in soundcard until I get a PUC2 soundcard next week. Testing with web presets from Jeff and Bojcha (Enlightened)

I am suffering with some jack xruns which I am resolving. I suspect the intel soundcard isn't up to doing much less than 512 samples/3 periods!

However, I have a slightly more annoying issue - basically if I do anything else with the computer (e.g. open a website), CPU usage in ST ramps from around 40% to 80% then the output buffer drops and the audio craps out. The terminal output starts complaining that jack is starving even though I'm not getting xruns. Eventually it starts to disconnect/connect from jackd.

Perhaps I'm expecting too much in terms of performance.

Any ideas how to bolster linux performance?

Hm, first one question: Can you try what happens if you disable the GUI (make the window as small as possible and then minimize it).

On Windows, the GUI thread runs at the lowest possible priority, on Linux all threads run at the same priority, at least for now.

I'll give this a go although it appears to be the CPU usage of the processing that suddenly starts to peak - the GUI usage stays at a constant 30%.

I can see ST has several threads - there is one running at 76 which I assumed was the GUI.

Doesn't seem to make any difference...

Steps to recreate:

Start qjackctl (with pasuspender to ensure no issues with pulse audio)
Run jackd at a reasonable 512/3 in realtime with a prio of 85
Start ST 64bit
Load Bojcha Enlightened web stream preset
Enable real-time, prio of 80

CPU load sits at 44% processing and 24% GUI (no audio playing through)

Open Firefox and access website such as speedtest...

Watch CPU in processing rise beyond 80% and everything crap out

So it seems that whenever something else wants CPU cycles, ST's own CPU usage peaks massively - even when it's not processing any audio. It's not apparent as a problem with presets not utilising high CPU but high-usage presets seem to amplify the problem.

I don't have a Linux system with me right now,
but this appears to be a priority issue. The CPU measurement in Stereo Tool actually shows the time spent in the processing code; if anything else stops ST it will show up as an increase. If ST would run at a high enough priority, other programs shouldn't block it.

2 other remarks:

1. If you CPU has Hyperthreading, any action on the shared core would cause a performance drop of about 35%. That's not enough to explain what you're seeing though.

2. I have seen on Windows that certain browser features (basically stuff that uses the GPU) cause big performance issues. In my tests, without running the browser I could get reliable I/O with a buffer of under 2 ms (in fact 0.7 ms is stable, but then there's no time to do any calculations); as soon as the browser started to use the GPU for heavy animations even at 30 ms I could still get some occasional hiccups.

Btw, I've never tried going this low with Jack on Linux so I'm not sure if it would work.

I'll do some further testing today. What you explain could explain this ramping up I'm seeing - I had always assumed ST ran at a fairly constant CPU load depending on what preset so was surprised to see the peaks.

The i5 only has four cores so it's quite possible the plugin-container (Flash sandbox), which seems to use an entire core, is blocking ST in some kind of way though.

That said, I've used rtirq to set the priority of the graphics and anything other than sound lower than ST and jackd so I'm still at a loss. I checked v 770 in case it was an issue with the newest build - doesn't seem to be.

I'll take a video soon.

I have tried upping buffers - to a point where ST's output buffer is over 1second but I can still break it.

https://www.youtube.com/watch?v=KSrx1dG9nQs

This is what I am seeing... With no audio (nothing in jack patched in) it will happily set there at 40%... The moment I try to do something else, the whole lot just goes tits up.

Is it simply that a quad core i5 isn't powerful enough to run ST and a web browser? Or is something else at play here?

Hm, just to rule something out: It seems to go wrong a wile after you start something heavy in the browser. Could it be that you CPU is heating up and slowing down? My previous laptop did that. So please check your CPU temperature (or just listen if the fan starts to make a lot of noise).

Beside that, I don't know how Linux handles heavy network traffic. If that's handled with a high priority it might also be causing this.


Note: In general, if you're going to use Stereo Tool for a radio station, the advise is to not run anything else on it. Definitely not a web browser, because they use all kinds of resources.

For one, if anything accesses the GPU, it can also use so much memory bandwidth that everything else gets slowed down.