script/: add cpu-map.sh to aid manual selection of CPU cores for threads for profiling

[perezjosibm]

This PR adds a new utility script

[script/cpu_map.sh]

Add a new tool to set the CPU core affinity for a group of threads within a process. This is useful when experimenting to set different groups of threads on different CPU cores.

Usage:
cpu-map.sh -p <process_PIDs comma separated> -n <process_Name> -g (optional) <by-group>

There are examples at the top of the script, which should make it easier to edit to suit for your own requirements.

• The following defines four group of threads, and the CPU cores they should be bound to:
  declare -A thr_grp_map=([alien-store-tp]="4-7" [rocksdb]="4-7" [bstore]="4-7" [cfin]="4-7" )
• The following indicates which CPU cores other threads not in the above groups should be bound to:
  free_cpu_avail="4-7"
• The next sentence defines a regular expression for the thread names that correspond to the above groups:
  proc_group_re="alien-store-tp|rocksdb|bstore|cfin"
• Finally, the following indicates not to change the affinity of the following group of threads:
  proc_ignore_re="crimson-osd|reactor|log|syscall"

This is an example of the execution and the resulting CPU core assignment:
cpu-map.sh -p $(pgrep crimson-osd) -g

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[athanatos]

I think I'm mostly just missing a bit of clarity on how to actually use this script -- slightly more specific examples would probably take care of that. Generally, I think this is fine to put in scripts/ and will be useful.

[athanatos]

This looks like it's lifted from seastar.git scripts/seastar-cpu-map.sh. That's fine, but let's update the examples to suggest how to use it specifically with crimson-osd or ceph-osd?

[athanatos]

Is the intention for the user to uncomment one of these sections depending on what they are doing?

[perezjosibm]

Yes, precisely, that is the intention. I thought that adding command line options at the script would make it confusing.
I'll add further examples asap.