System and user time would only be 99 or 100% if your process is processor intensive and the only process using the CPU on a single CPU system. Any time spent waiting for I/O, etc., would cause the %CPU to go down, since that's time that your program is "running" without using the CPU. Also, if other processes are competing for the CPU, then it will get a smaller percentage of the CPU time. For example, if there are two processes both competing for the processor, they would both get roughly 50% of the CPU time. Also, on multiple CPU systems, a single-threaded process will only run on one of the processors (at a time) and hence will only get a percentage of the total CPU time available. For example, on a 2-CPU system, your process would get up to and not more than 50% of the total CPU capacity. So, basically, your assumption is wrong. System and user time only represent the amount of CPU time that a process uses, and do not necessarily add up to the total elapsed time that a process has run and do not necessarily directly correspond to the % CPU time like your doing it. Something like this might be a little closer to reality: %CPU = (system + user) / (elapsed * num_CPUs) Thanks, Lyle -----Original Message----- From: gcc-help-owner@xxxxxxxxxxx [mailto:gcc-help-owner@xxxxxxxxxxx] On Behalf Of nyi nge Sent: Wednesday, July 14, 2004 4:45 PM To: gcc-help@xxxxxxxxxxx Subject: "time" command Hi I have run "time" command for my program and I got the following result. Percentage of CPU should be equal to user time + sys time divided by elapsed time (that should be 99%). But here I got only 18%. Any explanation? Can I still use User time as the correct result? User time (seconds): 52498.19 System time (seconds): 105.10 Percent of CPU this job got: 18% Elapsed (wall clock) time (h:mm:ss or m:ss): 14:37:00 Average shared text size (kbytes): 0 Average unshared data size (kbytes): 0 Average stack size (kbytes): 0 Average total size (kbytes): 0 Maximum resident set size (kbytes): 0 Average resident set size (kbytes): 0 Major (requiring I/O) page faults: 171 Minor (reclaiming a frame) page faults: 9258265 Voluntary context switches: 0 Involuntary context switches: 0 Swaps: 0 File system inputs: 0 File system outputs: 0 Socket messages sent: 0 Socket messages received: 0 Signals delivered: 0 Page size (bytes): 4096 Exit status: 0 __________________________________ Do you Yahoo!? New and Improved Yahoo! Mail - Send 10MB messages! http://promotions.yahoo.com/new_mail
