Issue #1: Generalize ssh play, up forks default to 25.

.gitignore

@@ -1 +1,2 @@
+config.yml
 hosts.ini

README.md

@@ -24,11 +24,14 @@ Other OSes may need a few tweaks to work correctly. You can also run the playboo
 
 ## Benchmarking - Cluster
 
-Make sure you have Ansible installed (`pip3 install ansible`), then set up a `hosts.ini` file in this directory based on the `example.hosts.ini` file.
+Make sure you have Ansible installed (`pip3 install ansible`), then copy the following files:
+
+  - `cp example.hosts.ini hosts.ini`: This is an inventory of all the hosts in your cluster (or just a single computer).
+  - `cp example.config.yml config.yml`: This has some configuration options you may need to override, especially the `ssh_*` and `ram_in_gb` options (depending on your cluster layout)
 
 Each host should be reachable via SSH using the username set in `ansible_user`. Other Ansible options can be set under `[cluster:vars]` to connect in more exotic clustering scenarios (e.g. via bastion/jump-host).
 
-Tweak any settings inside `config.yml` as desired (the most important being `hpl_root`—this is where the compiled MPI, ATLAS, and HPL benchmarking code will live).
+Tweak other settings inside `config.yml` as desired (the most important being `hpl_root`—this is where the compiled MPI, ATLAS, and HPL benchmarking code will live).
 
 Then run the benchmarking playbook inside this directory:
 

ansible.cfg

@@ -1,5 +1,6 @@
 [defaults]
 nocows = true
+forks = 25
 inventory = hosts.ini
 interpreter_python = /usr/bin/python3
 stdout_callback = yaml

config.yml → example.config.yml

@@ -2,14 +2,25 @@
 # Working directory where HPL and associated applications will be compiled.
 hpl_root: /opt/top500
 
+# Home directory of the user for whom SSH keys will be configured.
+ssh_user: pi
+ssh_user_home: /home/pi
+
+# Use this option if running on a single node.
+ram_in_gb: "{{ ( ansible_memtotal_mb / 1024 * 0.75 ) | int | abs }}"
+
+# Use this option if running on multiple nodes in a cluster; calculate manually.
+# ram_in_gb: "44"
+
+# Count the nodes for accurate HPL.dat calculations.
+nodecount: "{{ ansible_play_hosts | length | int }}"
+
 # HPL.dat configuration options.
 # See: https://www.advancedclustering.com/act_kb/tune-hpl-dat-file/
 # See also: https://hpl-calculator.sourceforge.net/HPL-HowTo.pdf
-nodecount: "{{ ansible_play_hosts | length | int }}"
-ram_in_gb: "{{ ( ansible_memtotal_mb / 1024 * 0.75 ) | int | abs }}"
 hpl_dat_opts:
   # sqrt((Memory in GB * 1024 * 1024 * 1024 * Node count) / 8) * 0.9
-  Ns: "{{ (((((ram_in_gb | int) * 1024 * 1024 * 1024 * (nodecount|int)) / 8) | root) * 0.90) | int }}"
+  Ns: "{{ (((((ram_in_gb | int) * 1024 * 1024 * 1024 * (nodecount | int)) / 8) | root) * 0.90) | int }}"
   NBs: 192
   Ps: 2
   Qs: 2

main.yml

@@ -31,10 +31,13 @@
       ansible.builtin.file:
         path: "{{ item }}"
         state: directory
+        owner: "{{ ansible_user }}"
+        group: "{{ ansible_user }}"
         mode: 0755
       loop:
         - "{{ hpl_root }}/tmp"
         - "{{ hpl_root }}/tmp/atlas-build"
+      become: true
 
     - name: Download MPI (Message Passing Interface).
       ansible.builtin.unarchive:
@@ -145,11 +148,11 @@
   tasks:
     - name: Generate an OpenSSH keypair.
       community.crypto.openssh_keypair:
-        path: /home/pi/.ssh/id_rsa
+        path: "{{ ssh_user_home }}/.ssh/id_rsa"
         size: 2048
 
     - name: Read out ssh pubkey from each host.
-      ansible.builtin.command: cat /home/pi/.ssh/id_rsa.pub
+      ansible.builtin.command: cat "{{ ssh_user_home }}/.ssh/id_rsa.pub"
       changed_when: false
       register: ssh_pubkey
 
@@ -160,7 +163,7 @@
 
     - name: Write all pubkeys to each host.
       ansible.posix.authorized_key:
-        user: pi
+        user: "{{ ssh_user }}"
         state: present
         key: "{{ item }}"
       loop: "{{ combined_ssh_pubkeys }}"
@@ -172,7 +175,7 @@
 
     - name: Accept hostkeys for each host on each host.
       ansible.builtin.command: >-
-        ssh pi@{{ item }} -o StrictHostKeyChecking=accept-new date
+        ssh {{ ssh_user }}@{{ item }} -o StrictHostKeyChecking=accept-new date
       loop: "{{ host_ips }}"
 
 - name: Run linpack benchmark.