No options to use isolated CPU cores

[pkumarg]

Hi,

I'm working on a Linux system with Realtime Kernel, and I have most of the core isolated by tuned. 'isolated' in general if you don't know is that Linux OS cannot use these cores to run anything until you explicitly specify.

Now I have around 32 cores, where system is running only on 2 cores, rest of the cores isolated for Realtime software to run. Now whenever I have to compile this big Realtime software, building takes too much as ninja-build only can run 2 cores. While others are just idle.

Please provide an option so that ninja-build can launch compiler threads on a user provided core list. Below can be examples
ninja --core-list=1-31
ninja --core-list=1,2,3,4-20,25-27

Thanks

[digit-google]

Try using Linux cgroups instead. For example, if you have systemd on your system: systemd-run --scope --property AllowedCPUS=1-31 ninja ... will do exactly what you're asking for.

[pkumarg]

Hi,

Thanks for quick answer but it looks like with this option also compilation spans only till non isolated cores:

In attached image you can see 'P' field, where cores 0,1,32,33 which are non-isolated are picked allocated only when I'm giving this command:
sudo systemd-run --scope --property=AllowedCPUs=0-31 ninja

Seems range 0-31 had no effect. Any ideas what could be happening.

I'll explore too.

Thanks though.

[digit-google]

Looks like cgroups / systemd-run is not working properly on your system. You could try verifying that by starting a scoped shell then looking at the content of /proc/cpuinfo to check that it reflects the range you gave, e.g.:

# Start a shell with a restrict CPU set, using `sudo` to escalate privileges to root
# then switching back to the current user.
sudo systemd-run --scope --property AllowedCPUs=0-7 sudo -u $USER bash -i

# This should only list 0 to 7, included.
grep -e '^processor:' /proc/cpuinfo 

[pkumarg]

Hi,

[user@linux build]sudo systemd-run --scope --property AllowedCPUs=0-19 sudo -u $USER bash -i
Running scope as unit: run-r077458d086134149bfa8d1933fa13228.scope

I couldn't come early one this. Just tried your hint, but still same. Once cores are isolated from OS via 'tuned' Linux GPS will not be knowing that it has these cores. May be that's why this scope thing is not working.

I have to explore about it.

More suggestions are welcome. Thanks for the suggestions so far.

Cheers !