[PlanetCCRMA] Question related to RT kernel

[Fernando Lopez-Lezcano]

On 01/07/2018 12:58 PM, Yann Collette wrote:
> Hello,

Hi!,

> I use Fedora 26 and I installed the RT kernel from ccrma repo.
>
> $ cat /proc/version
>
> Linux version 4.13.10-200.rt3.1.fc26.ccrma.x86_64+rt
> (mockbuild at planetccrma.stanford.edu) (gcc version 7.1.1 20170622 (Red
> Hat 7.1.1-3) (GCC)) #1 SMP PREEMPT RT Thu Nov 2 16:37:01 PDT 2017
>
>
> I changed /etc/security/limits.d/95-jack.conf
>
> $ cat /etc/security/limits.d/95-jack.conf
> # Default limits for users of jack-audio-connection-kit
>
> @jackuser - rtprio 90
> @jackuser - memlock unlimited
> @jackuser - nice -20
>
> #@pulse-rt - rtprio 20
> #@pulse-rt - nice -20
>
> And I added my user to the jackuser group.
>
> When I run realTimeConfigQuickSca, I've got the following report:
>
> $ realTimeConfigQuickScan
> == GUI-enabled checks ==
> Checking if you are root... no - good
> Checking filesystem 'noatime' parameter... found - warning
> / does not have the 'noatime' parameter set
> /home does not have the 'noatime' parameter set
> For more information, see
> http://wiki.linuxmusicians.com/doku.php?id=system_configuration#filesystems
> Checking CPU Governors... CPU 0: 'powersave' CPU 1: 'powersave' CPU 2:
> 'powersave' CPU 3: 'powersave'  - not good
> Set CPU Governors to 'performance' with 'cpufreq-set -c <cpunr> -g
> performance'
> See also: http://linuxmusicians.com/viewtopic.php?f=27&t=844
> Checking swappiness... 10 - good
> Checking for resource-intensive background processes... none found - good
> Checking checking sysctl inotify max_user_watches... >= 524288 - good
> Checking access to the high precision event timer... readable - good
> Checking access to the real-time clock... readable - good
> Checking whether you're in the 'audio' group... yes - good
> Checking for multiple 'audio' groups... no - good
> yes - good.
> Checking the ability to prioritize processes with chrt... yes - good
> Checking kernel support for high resolution timers... found - good
>
> Kernel with Real-Time Preemption... not found - not good
> Kernel without real-time capabilities found
>
> For more information, see
> http://wiki.linuxmusicians.com/doku.php?id=system_configuration#installing_a_real-time_kernel
>
> Checking if kernel system timer is set to 1000 hz... found - good
> Checking kernel support for tickless timer... found - good
> == Other checks ==
> Checking filesystem types... ok.
> ok.
> ** Set $SOUND_CARD_IRQ to the IRQ of your soundcard to enable more checks.
>    Find your sound card's IRQ by looking at '/proc/interrupts' and lspci.
>
>
> I am a little bit confused by this report ... A RT kernel without RT
> capabilities ???
>
> Kernel with Real-Time Preemption... not found - not good

This is weird...

> Kernel without real-time capabilities found
>
> Maybe the problem is related to realTimeConfigQuickScan..
>
> How can I check the realtime capabilities of this kernel ?

One way is to do this:

----
grep PREEMPT /boot/config-4.13.10-200.rt3.1.fc26.ccrma.x86_64+rt
----

This checks the existence of "PREEMPT" related kernel configuration 
options. The output should be similar to:

----
CONFIG_PREEMPT_RCU=y
CONFIG_PREEMPT_NOTIFIERS=y
CONFIG_PREEMPT=y
CONFIG_PREEMPT_RT_BASE=y
CONFIG_HAVE_PREEMPT_LAZY=y
CONFIG_PREEMPT_LAZY=y
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
# CONFIG_PREEMPT__LL is not set
# CONFIG_PREEMPT_RTB is not set
CONFIG_PREEMPT_RT_FULL=y
CONFIG_PREEMPT_COUNT=y
# CONFIG_DEBUG_PREEMPT is not set
# CONFIG_PREEMPT_TRACER is not set
----

The one to look for (mainly) is CONFIG_PREEMPT_RT_FULL, if it is set to 
"y" then full preemption is enabled and the RT patch is included, AFAIK 
this option is not available without it. I tried to test this by forcing 
the fc26 install on my fc24 laptop (yes, I know, OLD) and it finds the 
option. Weird.

The script (in PreemptRtCheck.pm) is checking for this so I don't know 
why it would fail.

-- Fernando

PS: sorry to not have yet an Nvidia compatible kernel on 27, argh... 
time time time...