[09:40] <johey> If my kernel hangs at boot when using lowlatency, how can I start tracking the problem down? Using Ubuntu 13.04 with official lowlatency kernel package.
[09:40] <johey> If started without quiet and splash kernel parameters, it just says "Loading Linux 3.8.0-31-lowlatency ..." then hangs at the purple screen.
[09:40] <johey> You can see a cursor or underscore at the line below, but it won't react on any keypress.
[09:40] <johey> Using a ThinkPad X1 Carbon, amd64 kernel.
[09:44] <smartboyhw> zequence_, your expertise^
[09:48] <johey> Good. That's a hard to find property. :)
[09:50] <smartboyhw> !kernel
[09:50] <smartboyhw> johey, though, linux-lowlatency is very simliar to linux in normal means
[09:51] <johey> Using the linux-generic is no problem. Booting perfectly. Lowlatency freeze totally.
[09:51] <smartboyhw> OK, that's a specific bug then
[09:51] <smartboyhw> johey, can you run "ubuntu-bug linux-lowlatency" within a terminal?
[09:51] <johey> I'm using it with other machines without problem.
[09:52] <johey> Ok, in a moment.
[10:30] <johey> smartboyhw: Bug reported. https://bugs.launchpad.net/ubuntu/+source/linux-meta-lowlatency/+bug/1232413
[10:30] <smartboyhw> johey, thanks
[10:31] <johey> smartboyhw: Currently I am not using Ubuntu Studio on this machine, but it is the same kernel package, isn't it?
[10:31] <smartboyhw> johey, yes.
[10:32] <johey> I am sorry not being able to give more details. I don't like reporting a bug only saying it just hangs, but what can I do...
[10:33] <johey> I am quite technically skilled, but I'm not a kernel hacker. If there are things I can do to help debugging, please feel free to ask.
[10:33] <johey> Last time I even compiled a kernel was 2.4.
[10:34] <smartboyhw> johey, wah:O
[10:34] <johey> Nowadays, it just works, you know... :)
[10:36] <johey> Are the lowlatency and generic kernel images built from the same source just with different configurations, or is the lowlatency patched?
[10:36] <smartboyhw> johey, same source
[10:36] <smartboyhw> different configrations
[10:37] <johey> Ok. So what I could do is trying to narrow down the set of configuration options until I know which one causes the hang... Would it help you think, or is it just one option to enable a large set of code?
[10:38] <smartboyhw> johey, dunno
[10:38] <smartboyhw> I'm not the kernel guy
[10:39] <johey> Right. That's zequence_.
[10:57] <Heyokha> Hi
[11:00] <smartboyhw> Hello Heyokha 
[11:01] <johey> smartboyhw: Do I have to use the lowlatency kernel to get realtime permissions for jack btw?
[11:06] <smartboyhw> johey, technically, as long as you're in the "realtime" group, you can get realtime permissions
[11:06] <smartboyhw> http://jackaudio.org/linux_rt_config
[11:07] <johey> I see. That might do it for me.
[11:07] <johey> I thought the group was audio.
[11:08] <johey> Mhm. adduser: The group `realtime' does not exist. .. Maybe this differ from ubuntu and ubuntustudio? Don't tell me I'm asking in the wrong channel... :)
[11:10] <smartboyhw> Technically, you are.
[11:10] <smartboyhw> !support | johey 
[11:11] <smartboyhw> johey, it might be the audio group for us
[11:11] <smartboyhw> I forgotten which:P
[11:12] <johey> Yes I know. I happened to ask about my kernel issue in almost all #ubuntu* channels, and this one gave the best hits. :)
[11:12] <smartboyhw> johey, it should be "audio" for us
[11:15] <johey> Ok. I will investigate that. Maybe I don't need the lowlatency. As long as I can keep latency <20ms without suffering from too many xruns I'm happy.
[12:28] <zequence_> johey: If you don't do any live processing at all, you don't need low latency
[12:28] <zequence_> johey: Just to confirm, the -generic that works is the same version as the -lowlatency that doesn't work?
[12:32] <zequence_> Ah, yes. I can see it is from the bug report
[12:32] <zequence_> It's very unlikely for there to be problems with -lowlatency that do not occur on -generic, as they are almost the same exact kernel
[12:33] <zequence_> johey: Earlier versions of -lowlatency works fine, right?
[12:34] <zequence_> smartboyhw: johey: We use the audio group for realtime privilege
[12:37] <zequence_> There's no lowlatency patchset
[12:37] <zequence_> johey: It would be great if you could try other version of linux-lowlatency
[12:39] <johey> zequence_: I've tried with the oldest version I find in the repos, namely 3.8.0-22 with same result.
[12:40] <zequence_> johey: Try something like a 3.2 instead
[12:40] <zequence_> https://launchpad.net/~ubuntustudio-kernel/+archive/linux-lowlatency-sru/+packages
[12:40] <johey> It's fully reproducible on this machine. Haven't successfully passed the kernel load step one single time. Although, on my technically most equal machine, the ThinkPad X220, this is no issue at all.
[12:41] <zequence_> Download manually, under linux-lowlatency-*
[12:41] <zequence_> the package called linux-image-*-lowlatency-*
[12:41] <johey> Ok, I'll try that.
[12:45] <johey> Just to ensure, I don't need the kernel header packages, right? The installation warns me about it.
[12:49] <johey> zequence_: 3.2.0-54-lowlatency hangs the same way.
[12:58] <johey> I managed to get realtime permissions without the lowlatency kernel, but after trying recording audio I realize I really need the lowlatency kernel.
[12:59] <johey> Cannot even manage to get free from xruns with 20 ms.
[13:02] <johey> 20 ms latency that is.
[13:49] <zequence_> johey: You don't need low latency unless you are doing software monitoring
[13:50] <johey> zequence_: Well, I actually am.
[13:50] <zequence_> 20ms IMO is too high anyway
[13:50] <zequence_> johey: Can't you monitor externally?
[13:50] <zequence_> What is it you are recording?
[13:50] <johey> I'm using live guitar effects.
[13:51] <johey> When recording the latency is of lower importance.
[13:55] <zequence_> johey: Check your /var/log/dmesg.0
[13:57] <johey> zequence_: Nothing is written to /var/log/dmesg.* when booting a lowlatency kernel.
[13:58] <johey> At least not enough to write it's own kernel version.
[13:59] <johey> I've never before seen a kernel hang this early. Not one single character is printed to the screen by the kernel.
[14:00] <johey> It seems like it hangs while it is copied to memory.
[14:00] <smartboyhw> That's a rare bug:O
[14:00] <zequence-work> johey: This is the diff between -generic and -lowlatency, prior to building http://paste.ubuntu.com/6167050/
[14:00] <zequence-work> In the config, that is
[14:01] <johey> Ok, but the CONFIG_PREEMPT=y enables a large chunk of code I would guess.
[14:02] <zequence-work> Might be the realtime patch hackers might be interested in solving this problem
[14:03] <johey> Where can I find them?
[14:03] <zequence-work> https://rt.wiki.kernel.org/index.php/Mailinglists
[14:04] <zequence-work> johey: You might want to try a realtime kernel as well
[14:05] <zequence-work> johey: http://wiki.linuxaudio.org/wiki/system_configuration#build_your_own_real-time_kernel
[14:05] <zequence-work> Some of the realtime patch has been included into the vanilla kernel. Bit by bit.
[14:06] <johey> Alright! The lowlatency and realtime are different pieces of code?
[14:06] <zequence-work> lowlatency is not a patch at all
[14:07] <zequence-work> linux-lowlatency is linux-generic, but with the preemtp configuration
[14:07] <johey> I'm sure the preemt used to be a patch... And I thought it came from the realtime code, but I'm likely wrong. I usually am. :)
[14:08] <zequence-work> As I said, the realtime patch has been included into the vanilla code, bit by bit
[14:09] <zequence-work> johey: I'd be interested to know if a realtime kernel would work for you or not
[14:09] <johey> Ok. Anyway, trying out a realtime kernel is the next step I think.
[14:09] <johey> I will let you know.
[14:09] <zequence-work> johey: Thanks
[14:09] <johey> I mean it's the next-next step. Trying AVLinux first.
[18:31] <johey> zequence-work: It also hangs with 3.10.10-rt.
[19:28] <johey> zequence-work: GAAAAHHH!! You know what... ThinkPad X1 Carbon is really well prepared for standing up against evil free software. Just disabling every option in the BIOS Security menu fixed the issue.
[19:31] <OvenWerks> figures.