CPU core reservation and Latency setting via config

CPU core reservation and Latency setting via config

[Neeraj Agrawal]

Hello,
Seeking advice on two separate issues. One of them may be just the documentation.

Setup is:
                Building via buildroot
                [Xenomai] Cobalt v3.0.10 is running over qemu with 2 CPUs.
                Linux version 4.14.111.
                bootargs: isolcpus=1 processor.max_cstate=0 intel_idle.max_cstate=0 nosoftlockup=0 rcu_nocbs=1 irqaffinity=0 tsc=reliable .....

Issue 1\ Latency setting:
Referring to https://xenomai.org/documentation/xenomai-3/html/man1/autotune/index.html
-enabling CONFIG_XENO_OPT_AUTOTUNE does create entry as '/dev/rtdm/autotune' in target.
-setting XENO_OPT_TIMING_SCHEDLAT does NOT reflect in '/proc/xenomai/clock/coreclk'
-enabling BR2_PACKAGE_XENOMAI_ANALOGY does build autotune application, but running it on target also does NOT reflect XENO_OPT_TIMING_SCHEDLAT setting in '/proc/xenomai/clock/coreclk'

Is my expectation correct that statically defined gravity values should reflect in coreclk?
-If so, how could it be achieved?
-If not, then how to verify if the values are set/used correctly?


Issue 2\ CPU cores distribution:
If bootargs have both ("isolcpus=1 maxcpus=1"), ie:
                isolcpus=1 maxcpus=1 processor.max_cstate=0 intel_idle.max_cstate=0 nosoftlockup=0 rcu_nocbs=1 irqaffinity=0 tsc=reliable .....
Then i get a boot time crash. [Could not collect the log, but crash indicate somewhere in i-pipe]
Idea behind this is to force Linux to use 1st CPU, there by leaving 2nd CPU dedicated for Xenomai. Either of the entry alone works (but not together).
[Also tried xenomai.supported_cpus=0x02 without success].

Any advice whether it is feasible to boot Xenomai with both these bootargs on my setup?
If so, where i could look into for bootup crash?


Regards
Neeraj

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Re: CPU core reservation and Latency setting via config

[Jan Kiszka]

On 25.08.21 10:16, Neeraj Agrawal via Xenomai wrote:
> Hello,
> Seeking advice on two separate issues. One of them may be just the documentation.
> 
> Setup is:
>                 Building via buildroot
>                 [Xenomai] Cobalt v3.0.10 is running over qemu with 2 CPUs.
>                 Linux version 4.14.111.
>                 bootargs: isolcpus=1 processor.max_cstate=0 intel_idle.max_cstate=0 nosoftlockup=0 rcu_nocbs=1 irqaffinity=0 tsc=reliable .....

Architecture?

> 
> Issue 1\ Latency setting:
> Referring to https://xenomai.org/documentation/xenomai-3/html/man1/autotune/index.html
> -enabling CONFIG_XENO_OPT_AUTOTUNE does create entry as '/dev/rtdm/autotune' in target.
> -setting XENO_OPT_TIMING_SCHEDLAT does NOT reflect in '/proc/xenomai/clock/coreclk'

There is apparently a translation issue. While the config help says you
should specify in nanoseconds, the value is actually accepted in clock
cycles (TSC in case of x86).

Philippe, all those hard-coded values in
kernel/cobalt/arch/*/*/include/asm/xenomai/calibration.h are actually in
ticks? Or are they also in ns, and we need to convert them to ticks as well?

> -enabling BR2_PACKAGE_XENOMAI_ANALOGY does build autotune application, but running it on target also does NOT reflect XENO_OPT_TIMING_SCHEDLAT setting in '/proc/xenomai/clock/coreclk'

That is likely a buildroot topic. Please address via that community
first (provided you meant BR2_PACKAGE_XENOMAI_AUTOTUNE, not ANALOGY).

> 
> Is my expectation correct that statically defined gravity values should reflect in coreclk?
> -If so, how could it be achieved?
> -If not, then how to verify if the values are set/used correctly?
> 
> 
> Issue 2\ CPU cores distribution:
> If bootargs have both ("isolcpus=1 maxcpus=1"), ie:
>                 isolcpus=1 maxcpus=1 processor.max_cstate=0 intel_idle.max_cstate=0 nosoftlockup=0 rcu_nocbs=1 irqaffinity=0 tsc=reliable .....
> Then i get a boot time crash. [Could not collect the log, but crash indicate somewhere in i-pipe]

Indeed, maxcpus=1 crashes on x86 with I-pipe. Not with dovetail (5.10),
though. With maxcpus=1, we start with any core > 0 being offline, and
that is likely not supported by I-pipe. Taking cores offline later on is
supposed to work, though.

> Idea behind this is to force Linux to use 1st CPU, there by leaving 2nd CPU dedicated for Xenomai. Either of the entry alone works (but not together).
> [Also tried xenomai.supported_cpus=0x02 without success].

Try only isolcpus and possibly xenomai.supported_cpus (if you like to
reduce the impact of Xenomai on non-RT CPUs).

Jan

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