$> ps waux --sort=-pcpu

If you piped the result into the head command, you can limit the result to the n entries with the highest CPU usage.

$> ps waux --sort=-pcpu | head -n 10

In this example you will see the ten most CPU-consuming processes on the machine. The ‘–‘ before pcpu results in a descending order.

Example output:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
kd249069  2686 11.5  4.9 1462144 1230768 pts/1 S+   01:30 111:32 /usr/lib64/php5/5.4.38/bin/php product_import.php -target products -testmode
kd176735  2302  7.1  1.0 400296 259460 ?       R    May07 139:53 /usr/bin/php5-5.3.8-cgi
kd176735  2303  6.3  0.9 385040 238712 ?       S    May07 124:50 /usr/bin/php5-5.3.8-cgi
kd176735  2301  5.9  1.0 396320 255652 ?       S    May07 116:38 /usr/bin/php5-5.3.8-cgi
kd176735  7074  5.7  0.7 319384 176952 ?       S    May07  82:06 /usr/bin/php5-5.3.8-cgi
kd176735 30571  5.7  0.6 307956 167248 ?       S    May07  98:18 /usr/bin/php5-5.3.8-cgi
kd176735 30573  5.5  0.8 353852 211716 ?       S    May07  93:43 /usr/bin/php5-5.3.8-cgi
kd176735 30572  5.4  0.8 341068 198780 ?       S    May07  93:18 /usr/bin/php5-5.3.8-cgi
kd176735 29817  5.3  0.8 345640 202672 ?       S    May07  67:20 /usr/bin/php5-5.3.8-cgi

To see what happens in a particular process you can observe the process with strace.