how-many-subshells/how-many-subshells.sh

#!/usr/bin/env bash

NPROC=$(grep -c ^processor /proc/cpuinfo)
RESULTS_FOLDER=$(mktemp --dir)

# Checking ulimit
if [[ $(ulimit) == "unlimited" ]];then
  ULIMIT_YES="no"
  while [[ $ULIMIT_YES == "no" ]]
  do
    read -p "ulimit is unlimited. This may not go well for the system. Are you sure? (yes/no): " ULIMIT_YES
    if [[ $ULIMIT_YES == "yes" ]];then
      break
    elif [[ $ULIMIT_YES == "no" ]];then
      exit
    fi
  done
fi

# Run the job with n number of nprocs
find ./jobs -type f -name "*.sh" | \
while read JOB_NAME
do
  printf "Starting on job $JOB_NAME...\n"
  SCALE=1
  CURRENT=9998
  BEFORE=9999
  RESULT_FILE="$RESULTS_FOLDER/$(basename $JOB_NAME)"
  #printf "Result file: $(readlink -f $RESULT_FILE)\n"

  # Keep scaling up until the runtime is slower than the previous result
  while [[ $(echo "$CURRENT < $BEFORE" | bc) -eq 1 ]]
  do
    BEFORE=$CURRENT
    PARALLEL=$(( $NPROC * $SCALE ))
    CURRENT=$( \
      /bin/time --format "%e" \
        bash -c "seq 1 10000000 | xargs -P $PARALLEL bash $JOB_NAME >/dev/null 2>&1" 2>&1 | \
        tee -a $RESULT_FILE \
    )
    (( SCALE++ ))
  done

  # Display the results 
  printf "nproc\tseconds\n"
  awk \
    -v nproc="$NPROC" \
    '{print NR*nproc, "\t", $0}' \
    $RESULTS_FOLDER/*

done

# Clean up
rm -rf $RESULTS_FOLDER