[svlug] CPU load and real world value

Robert Freiberger rfreiberger at gmail.com
Wed Mar 23 15:36:20 PST 2016


Hello Michael,

Thanks for the reply and I have used top plus the other variants in the
past. The issue I should have explained clearly in the first e-mail is
finding the root cause for high CPU load and if it's really a valid
measurement of system performance. At my job, we have a majority of alerts
that are focused on application metrics (latency and api calls), system
level (free memory, CPU load, disk space), and finally synthetic checks
(user simulation).

We will semi-frequently find CPU load spikes on the host, but nothing else
is alerting. Taking a look at the load trending, through sar, it's jumping
from 1~4 to 20~30 within minutes, holds this for about an hour, then drops
back to the previous levels. While I check the various metrics from our
monitoring, I do not see anything that is obvious to the rise.

My knowledge within the cpu calls and how the system works is very limited,
wonder if there is a good reference I should look for as a starting guide?

Thanks,
Robert

On Sun, Mar 20, 2016 at 1:05 PM Michael Eager <eager at eagercon.com> wrote:

> On 03/18/2016 04:48 PM, Robert Freiberger wrote:
> > Hello,
> >
> > I still consider myself pretty new to the world of UNIX/Linux, and find
> that when I investigate an
> > issue with CPU load, it's very difficult to trace the issues. Unlike
> performance problems with
> > network or NFS, where I can test latency with simple commands, load
> appears to be much harder to
> > test in real time.
>
> Are you familiar with "top" or the graphical variant "htop"?
> Both will give a real-time display of current system load
> and activity.  KDE and Gnome have graphical monitors for CPU
> utilization and other activity, such as memory or network use.
>
> Tecmint.com has an article about 20 different tools which can
> be used to monitor Linux performance.
>
> > Is there any recommendations how to really investigate this and how
> effective is CPU load to a
> > systems health?
>
> It's not clear what you are investigating.  Do you have a problem
> or are you simply curious?
>
> High or low CPU utilization is not a cause or solution to poor
> performance.  If you are running at 80% CPU, that means that the
> CPU is idle 20% of the time.  Any program which is ready to run
> while the CPU is idle will be dispatched.  On most systems, reducing
> CPU load to 60% will not make programs run faster, it will just increase
> your idle time.  (This may not be true if you are running CPU-intensive
> programs like transcoders or video editors.)
>
> More interesting is load averages displayed by top/htop and
> uptime.  This is the average number of runnable processes which
> are waiting at any particular time.  High load averages result
> in poor responsiveness.
>
> --
> Michael Eager    eager at eagercon.com
> 1960 Park Blvd., Palo Alto, CA 94306  650-325-8077
>
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