RHEL AS 4 U2 Slow 2006-02-07 - By Rick Stevens
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On Tue, 2006-02-07 at 17:29 -0500, Brenda Radford wrote:
> Rick Stevens wrote:
I'm cleaning up the message a bit...there's a lot of cruft we don't
need to deal with anymore.
> >There's nothing obvious there. What you really need to do is run
> >"top" and look at the top few processes listed there (you can usually
> >ignore the "init", "top" and "X" processes) and see what's sucking up
> >the CPU time. Watch the "%CPU" and %MEM" columns and find the process
> >that's got the highest "%CPU" bit. That's the one we need to look at.
> >
> >Also pay attention to the bit that looks like this:
> >
> >Cpu(s): 4.6% us, 0.0% sy, 0.0% ni, 94.4% id, 0.0% wa, 1.0% hi,
> >0.0% si
> >
> >as it shows a summary of where the CPU is spending its time:
> >
> >"us" = user state
> >"sy" = system state
> >"ni" = non-interruptible sleep
> >"id" = idle
> >"wa" = I/O wait state
> >"hi" = hardware interrupts
> >"si" = software interrupts
> >
> >Even if you don't see a process sucking up a lot of CPU, but you see
> >the CPU spending a lot of time in the "wa" state, then you have a disk
> >problem. Look in the process list for processes in the "D" state.
> >
> >
> >
> >
> Rick,
>
> From top, on two different days:
>
> [brenda@(protected) ~]$ top
>
> top - 20:40:49 up 11 min, 2 users, load average: 0.03, 0.05, 0.06
> Tasks: 83 total, 1 running, 82 sleeping, 0 stopped, 0 zombie
> Cpu(s): 2.3% us, 0.0% sy, 0.0% ni, 97.7% id, 0.0% wa, 0.0% hi, 0.0% si
> Mem: 905760k total, 306536k used, 599224k free, 18996k buffers
> Swap: 1799232k total, 0k used, 1799232k free, 180724k cached
>
> [brenda@(protected) ~]$ top
>
> top - 15:31:16 up 35 min, 4 users, load average: 0.24, 0.07, 0.02
> Tasks: 89 total, 1 running, 87 sleeping, 0 stopped, 1 zombie
> Cpu(s): 1.3% us, 0.0% sy, 0.0% ni, 98.7% id, 0.0% wa, 0.0% hi, 0.0% si
> Mem: 905760k total, 396168k used, 509592k free, 23224k buffers
> Swap: 1799232k total, 0k used, 1799232k free, 244368k cached
>
> The only time the CPU showed any activity in the I/O wait state was when
> top was first started,
> at the 1-4% level, and only for an instant. It immediately went back to
> 0.0%. The only other
> processes that showed up at the top of the list (besides those you
> mentioned) were gnome-terminal,
> hald, and rhn-applet-gui, but they only used tiny amounts of CPU and
> MEM, even with 4 or 5
> terminal windows open (hence the 4 users).
>
> The more times I ran top, the more Memory it reported used (in the top
> header). It went up to more than
> 4XX,XXX used before I was finished, after running top and ps ax
> numerous times.
That's normal and nothing to worry about. Start worrying if you see
the "Swap: 0k used," thing start to go non-zero. That means you're out
of memory and the system has to swap things from memory to disk and back
to run them. That slows the machine down a LOT.
> I didn't have any processes in the "D" state.
Ok, so we don't seem to have an I/O wait state issue. I did notice a
zombie process there in the second top report. I'm curious as to which
process that is and what its parent is. Try doing a "ps ax" and find
the process that's in a "Z" state.
> Any ideas?
Well, it doesn't seem to be process or memory related. It could be
context switching issues. Try doing a "vmstat 5" for, say a minute,
then CTRL-C to get out of it. Look at the "cs" column towards the
right. If that gets to 5 digits, we have something that's causing
context switch problems and there's a bit more investigation we need
to do.
Also look at the output of "dmesg" for clues.
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --
- Rick Stevens, Senior Systems Engineer rstevens@(protected) -
- VitalStream, Inc. http://www.vitalstream.com -
- -
- We are born naked, wet and hungry. Then things get worse. -
-- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- ---- --
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