Date: Fri, 5 Feb 2010 15:28:40 -0600 From: Dan Nelson <dnelson@allantgroup.com> To: Linda Messerschmidt <linda.messerschmidt@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: ps "time" field jumps backward Message-ID: <20100205212837.GA43582@dan.emsphone.com> In-Reply-To: <237c27101002050857r78003779mb41eae44f850829b@mail.gmail.com> References: <237c27101002050857r78003779mb41eae44f850829b@mail.gmail.com>
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In the last episode (Feb 05), Linda Messerschmidt said: > For most of 7.2, on up to a 7.3-PRERELEASE built yesterday, I've noticed > that the "time" field reported by ps and top jumps around for some > processes. I've particularly noticed it with MySQL. > > Here are some repeated ps results (ps axo pid,time,wchan,comm) for the > same process over a few minutes: > > 1647 0:08.06 ucond mysqld > 1647 0:08.06 ucond mysqld > 1647 0:08.06 ucond mysqld > 1647 0:08.06 ucond mysqld > 1647 0:08.07 ucond mysqld > 1647 0:10.24 wdrain mysqld > 1647 0:08.08 ucond mysqld > 1647 0:09.25 - mysqld > > It's like when it starts working it builds up time, but as soon as it > goes back to ucond, it resets back to the earlier value. By default, ps only lists one thread when listing threaded processes, and if it's anything like top, the CPU column seems to be randomly picked from one thread. Try running "ps axHo pid,lwp,time,wchan,comm" instead (add H and lwp). That will print the individual threads, plus the thread id so you can track them across runs. You should see one thread with a CPU value of "8.08" (or so), and other values for the rest. Ideally, top and ps would total up all the per-thread CPU counts when displaying the per-process numbers, but it doesn't seem to. -- Dan Nelson dnelson@allantgroup.com
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