[asterisk-users] Large system seeing single CPU core spiking

Tue Sep 14 12:55:30 CDT 2021

On Tue, Sep 14, 2021 at 9:19 AM Dan Cropp <dan at amtelco.com> wrote:

> Thank you George.
>
>
>
> It is using local file based configuration files.
>

Well, that's good at least.  It eliminates the database layer which can be
troublesome in virtualized environments, especially if a SAN and/or a
remote database server is used.

>
>
> Other factors.
>
> We run Asterisk in realtime mode to allow it to run as fast as possible.
>

Running at "realtime" level is usually NOT a good thing for Asterisk and
rarely needed when there are adequate resources.  Let's say you have a
local DNS resolver running.   If the system is stressed, Asterisk could
actually starve the resolver of resources, which then causes Asterisk to
back up waiting for DNS resolution to complete.  We've seen this happen
when using a database backend for configuration.  Someone thinks "I'll just
give Asterisk more resources" forgetting that Asterisk needs the database
engine to run.

>
>
> I just learned customer upgraded to 24 CPU cores.  Although, I’m not sure
> they actually assigned 24 physical cores to this machine or just increasing
> Hyper-V values.
>

How is this VM's priority versus other VMs on the same cluster?  Just
because it has 24 threads doesn't mean it's got 24 threads dedicated.  Does
using a realtime priority in the VM trickle down to Hyper-V's hypervisor's
resource management algorithms?

>
> I will monitor for additional information and see if the customer will
> allow me to capture a coredump when problems are happening.
>
> Waiting for them to report an incident.
>
>
>
> Here is a small sample of the system right now (24 cores), to the best of
> my knowledge it’s running fine.
>
>
>
> top -p 1509 -n 1 -H -b
>
> top - 15:06:32 up  9:06,  2 users,  load average: 6.02, 5.59, 5.26
>
> Threads: 1709 total,   8 running, 1701 sleeping,   0 stopped,   0 zombie
>
> %Cpu(s):  3.1 us,  2.5 sy,  0.0 ni, 94.3 id,  0.0 wa,  0.0 hi,  0.1 si,
> 0.0 st
>
> KiB Mem : 32143072 total, 29750072 free,  1016132 used,  1376868 buff/cache
>
> KiB Swap:  8388604 total,  8388604 free,        0 used. 30697060 avail Mem
>
>
>
>    PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND
>
>   1830 root     -11   0 13.741g 493680  28828 R 99.9  1.5 174:13.39
> asterisk
>
>   1541 root     -11   0 13.741g 493680  28828 R 14.3  1.5  20:03.30
> asterisk
>
> 33601 root     -11   0 13.741g 493680  28828 S  9.5  1.5   0:16.30 asterisk
>
> 46605 root     -11   0 13.741g 493680  28828 S  9.5  1.5   0:30.06 asterisk
>
>   2295 root     -11   0 13.741g 493680  28828 S  4.8  1.5  12:25.50
> asterisk
>
>   2297 root     -11   0 13.741g 493680  28828 S  4.8  1.5   1:10.59
> asterisk
>

There's definitely one thread that's pegging a CPU.  If that thread is one
of the few "singleton" threads, that can be an issue.  What does "core show
taskprocessors" indicate?  Are there any that are hitting their limits?

>
>
>
>
> *From:* asterisk-users <asterisk-users-bounces at lists.digium.com> *On
> Behalf Of *George Joseph
> *Sent:* Tuesday, September 14, 2021 9:39 AM
> *To:* Asterisk Users Mailing List - Non-Commercial Discussion <
> asterisk-users at lists.digium.com>
> *Subject:* Re: [asterisk-users] Large system seeing single CPU core
> spiking
>
>
>
>
>
>
>
> On Tue, Sep 14, 2021 at 8:07 AM Dan Cropp <dan at amtelco.com> wrote:
>
> I am working with a very large customer running Asterisk with PJSIP.
> Systems total channels have been over 2500 (which includes hundreds of
> local channels and ConfBridges) when the issues occur.
>
> It’s running on a Hyper-V VM with 12 CPU cores.
>
> Things work fine most of the time.
>
>
>
> They periodically see 10-30 minute periods where audio starts sounding
> like jitter buffer type issues.  Can literally have someone spelling their
> name and a ConfBridge recording of it shows the audio is missing a letter
> or two.
>
> The odd part is another system (not running Asterisk) was handling these
> calls previously.  The overall network has plenty of bandwidth (as
> evidenced by another system able to handle the call volume)
>
>
>
> One area that has perplexed us is when using htop, we see a single CPU
> core will spike to 100%.  Which core does keep changing.
>
>
>
> Asterisk is definitely the process using the vast majority of the CPU
> cycles.
>
>
>
> We recently found a setting on Hyper-V networking SR-IOV which improved
> things.  Prior to changing this setting, we were seeing SIP OPTIONS
> packets/responses would occasionally take more than 3 seconds causing
> devices to drop and come back online.
>
>
>
> We have configured a similar system running at Amazon handling far more
> traffic and can’t get the single CPU core to spike.  Only small static pops
> during the calls.
>
>
>
> The sheer scale of the system is making it hard to diagnose the problem.
>
>
>
> Any thoughts on how to diagnose what is causing the single CPU core to
> spike?
>
> Any thoughts on how to diagnose the problem?
>
> Any other thoughts/comments?
>
>
>
>
>
> The first thing I'd do is see where the CPU is spending time: userspace,
> system, nice, wait, etc.
>
> Is it actually the asterisk process consuming the CPU?
>
> Is Asterisk running with local file-based configs, local database, remote
> database, etc?
>
>
>
> If call quality is really bad already and your customer agrees, you could
> try the following the next time it happens...
>
>  1. Run "top -p `pidof asterisk` -n 1 -H -b" to get a list of all of
> Asterisk's threads and their CPU utilization.
>
>  2. Run ast_coredumper with the --RUNNING option.  This will pause
> Asterisk while the dump is being generated!
>
>  3. See if you can correlate the high cpu thread IDs from the top output
> to the threads listed in the coredumper's -brief.txt file.
>
>
>
> That _may_ give you an idea of where to look.
>
>
>
>
>
>
>
> Dan
>
>
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>
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> _____________________________________________________________________
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>
> Check out the new Asterisk community forum at:
> https://community.asterisk.org/
>
> New to Asterisk? Start here:
>       https://wiki.asterisk.org/wiki/display/AST/Getting+Started
>
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