On Wed, 2 Oct 2019, Mike Squires wrote:
The short answer here is that if I can use a generic kernel then Ubuntu Studio works across all of the PCs on which I need to run it; the low latency kernel, however, makes using versions 18 and 19 too slow for my needs.
The real question is what you wish to achieve with your system. The goals of lowlatency and throughput are not the same. In fact high throughput in general probably makes for poor lowlatency performance. If low latency is not a hard requirement for your use, then install a generic kernel and be happy. Yes it will be faster in some cases with some systems. Or to put it another way, the lowlatency kernel will always be at least a little bit slower than the generic kernel... on some systems it will be much more noticable.
So, end of story? No not really. On a single core atom processor running at 0.8Ghz (800 Mhz) the speed difference between generic and lowlatency is really not noticable. It can only deal with rather small packets anyway with only 2G Ram and a smaller data bus etc. One of the ways that a high powered server cpu with lots of cores can be "faster" or have greater throughput (how speed is normally measured) is to use really large packets and more the whole packet at once... however, if you have a high priority audio process that is stopping that file transfer every 128 samples so it can do a very small file transfer before that big transfer starts agian, then that large packet is effectively broken down into a large number of small packets being transfered. Each of those small packet portions may take as long as several packet portions would _if_ they were all sent as one packet because of the overhead of context change etc.
"Oh but I wasn't doing audio at the same time as the file transfer". Is that true? is Jack running silently? Even if no client is hooked to jack, if it is running and the packet size is 128 samples, then the device irq is firing every 128 samples without fail anyway. So one way to test this is to A) shut jack off while doing high speed file transfers (does that make it faster?) B) set jack to 1024 sample buffers or higher when it is only being used for listening to youtube. You will notice if you play with it much that hdmi audio has very large buffers as a minimum size. They will not accept 256 sample buffers, they are too small. That is he reason computers are not designed for audio... esspecially lowlatency audio. I have read some of the Intel specs for latency. In those specs "low latency" is 30ms... normal latency is higher. making a PC do low latency audio is hard and in some cases it is not really possible with some hardware. Having many cores should in theory help, but in the end does not as they all have to access the same memory. In a file transfer situation, it is main memory use that counts. Audio too uses that main memory and it has to access it on schedule whithin the time limits the buffersize puts on it.
Having said that... thankyou for reminding me... my machine was feeling slow and I am realizing I have the buffer size set quite slow when I don't need it to be.
I have been far too long winded on this, but this is not a bug that I can see. I do suspect there are ways of doing things better for high memory, high core count machines but I am not well versed with them. I know setting aside a core or two just for Audio is one of them. I am even aware that some people run a generic kernel on most of their system with a second real time kernel on a few cores. I have never done this and don't know where to look for it.
-- Len Ovens www.ovenwerks.net -- ubuntu-studio-devel mailing list ubuntu-studio-devel@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-studio-devel
