Debugging CPU usage in Nginx

[Clima Gabriel]

If your Nginx is compiled with debug symbols you may see some useful info
`perf top`

On Mon, Aug 12, 2024, 6:24 PM Brad Patton <brad at wordkeeper.com> wrote:

> Hi all,
>
> About 2 months ago the CPU usage on 1 of our servers started going crazy.
> All of a sudden, Nginx itself started using about 6x the CPU power to serve
> requests with no increase in traffic at all.  It's a dramatic difference
> and it's directly attributed to Nginx, not PHP, Mariadb, or anything else.
> I can show you a lot of graphs and data showing the problem if needed so
> let me know if you would like to see more.  🙂
>
> The only OS updates during the week prior to the issue starting were to
> PHP.  We're currently running Nginx version 1.27.0 and we were on 1.25.5
> when it started.  In addition to those updates, we've run several test
> builds where we disabled certain modules just randomly trying to isolate
> the issue.
>
> I was starting to think that the issue had something to do with our
> configuration, even though that didn't change at the start of the issue
> either, but then I ran a test in a Fedora 40 container and it solved the
> problem.  Unfortunately, I could only run that test temporarily, but the
> results were clear.  The same exact build with the same exact configuration
> works fine in Fedora 40 but takes about 6x the CPU power to serve the same
> requests in Centos Stream 9.
>
> That makes me think there is either some bug in Centos 9 or a bug in Nginx
> that only happens in Centos 9.  Does anyone have any thoughts on how to
> find out exactly what in Nginx is causing the much higher CPU usage?
>
> If not, would you like to see more information about the problem?  If so,
> what?
>
> Thanks!
> Brad
>
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