Robert

Thanks for all of your information on the low latency kernel. I've used x2go for several years and one use-case I've had was to install the x2go server onto either Amazon's AWS EC2 or on Digital Ocean to support remote desktops for K-12 schools that I do volunteer work for.

Clients have always been a mix of Win7, Mac or Ubuntu linux.

Really the only issue has been video streaming which for K-12 is important because alot of learning content online consists of video.

In the past I've tried using larger "compute" instances (8-16 core) in those clouds thinking perhaps the video encoding/transmission load was the cause but that only improved things marginally.

I tried higher bandwidth links... same marginal improvement.

It didn't matter what client they used (mac, win7 or linux) the video content viewing results was more or less the same for each.
That's why I am thinking maybe only the server-side "may" be required to have the low latency kernel??

I got them all so the streaming video (say youtube) wasn't awful but it wasn't the same as watching the video on a dedicated PC instead of thru the x2go virtual desktop.

But i guess I never suspected the linux kernel introducing delay/jitter to the point of being the cause.

It may take a while until I can get to it but I'll try and set up a test with one of those clouds and have the x2go server-side ubuntu utilize the low latency kernel you described and see what happens with each client.

This would be great if that turns out to be the source of streaming video jerkiness for cloud based remote desktops. I'll post something to the x2go alias when I find out what happens.

thanks again.

Brian

On Wed, Apr 1, 2015 at 5:55 PM, Robert Dinse <nanook@eskimo.com> wrote:

In Ubuntu, they build low latency kernels and make them available as
part of the distribution but not installed by default.

On my workstation, which is an old Mac-Pro 1,1 with quad Xeon CPU's and
4 GB of RAM, I had Ubunto 14.04 installed then upgraded to 14.10. I had
Wine installed and under Wine I ran WinAmp to play music. WinAmp sometimes
skipped, and also when I upgraded to 14.10 which came with a 3.16.x kernel,
I had issues with the Nvidia drivers for my old 7300 GT card.

To solve those issues I ended up building a 3.18.9 kernel and built it
with kernel preemption enabled, which is how Ubuntu builds their low latency
kernels. That solved both my issues with Nvidia drivers and with WinAmp
stuttering but it did not fix the issues of video being jerky over X2Go, and
I had pretty much written that off to my Comcast connection anyway.

But given how much smoother things went on my workstation, I decided to
try installing the low latency kernel on the server and then tried watching
some Youtube videos that had previously been jerky (audio okay but video
jerky) and found that it made the video smooth.

So my guess is you probably need it on both, but since I haven't tried
it on the server only I can't say for sure.

The kernel on the server isn't custom built, it's one of the low latency
kernels provided by Ubuntu (I used synaptic package manager to select and
install, rebooted, then removed the old).

On the Mac I don't know. I had so much problems with X2Go on my Mac, even after installing the XQuartz server, that is one of the reasons I installed Ubuntu on it and stopped using MacOS. Got tired of the spinning beach ball, got tired of having zero games available. I liked the Dock but that's about it. Mac's approach of just throw enough hardware at it and it will be acceptable works if you have infinite money, I don't.

With respect to Windows, I only have an old antique XP machine that I use
for some games, don't really know how it would work with video over X2Go so
can't answer that one.

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On Wed, 1 Apr 2015, brian mullan wrote:

Date: Wed, 1 Apr 2015 17:36:06 -0400
From: brian mullan <bmullan.mail@gmail.com>
To: Robert Dinse <nanook@eskimo.com>
Cc: x2go-user@lists.x2go.org
Subject: Re: [X2Go-User] Jerky Video Fixed

Robert this is very interesting.. mainly because I wasn't aware there was
such a thing as a low latency kernel. Guess with linux you are always
learning. However, I have an experimental question. Is it just the kernel
on the video transmitting side, the client/receiver side or both that the
low latency kernel has this impact? Also, if the video server side is
linux with a low latency kernel then what would a client running x2go on a
mac or a windows 7 machine experience since neither utilize a linux kernel
?
Thanks for sharing as I had always figured it was a latency problem but
I assumed it was 100% due to the network itself.
Bria
On Apr 1, 2015 5:23 PM, "Robert Dinse" <nanook@eskimo.com> wrote:

I hope I've done this in a way that doesn't steal anyone else's
thread.

A while back someone posted that they had somewhat jerky video through
x2go, and I posted that if I watched someone on youtube over an x2go
connection, with a 20 mbit/s cable connection, on a Ubuntu 14.10 client
accessing a Ubuntu 14.04.2 LTS server, I also had some jerkiness to the
video.

I have installed low latency kernels on both machines now and that
eliminated the jerkiness. I can now watch a youtube video on a remote
machine
and have it display smoothly even with the highest quality setting set.

Just posting this so if others are experiencing this problem this may
be
a viable fix for them.

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Eskimo North Linux Friendly Internet Access, Shell Accounts, and Hosting.
Knowledgeable human assistance, not telephone trees or script readers.
See our web site: http://www.eskimo.com/ (206) 812-0051 or (800) 246-6874
.
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