Re: [HTCondor-users] HTCondor/cgroups: limiting CPUs/pinning processes to CPUs with hyperthreaded CPUs

[Bob Ball <ball@xxxxxxxxx>]

Pinning to a core is a different beast than is limiting the number of cores.  cgroups limits, it does not pin.

bob

On 2/4/2016 10:00 AM, Thomas Hartmann wrote:

Hi all,

I have a more technical question regarding cgroup support in
HTCondor/cgroups in general.

If a I understand the cgroup documentation correctly, a cgroup cannot be
limited to a "general number of cores" but can only be pinned to certain
cores. I.e., limiting the number of cores for a cgroup means to pin the
cgroup to as many dedicated cores on the system, or?
So, I guess the startd pins a job with core limit correspondingly in a
cgroup to cores, or?

Is this actually a drawback, that processes cannot be switched between
cores (does the CPU would move anyway processes between cores?)?
How does actually a hyperthreaded system would look like - if a process
is pinned to "a hyperthreaded core", I guess the process would be moved
over the physical cores by the CPU, or?

Cheers and thanks,
  Thomas

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