Re: 120k context switches on GlsuterFS nodes

mabi <mabi@xxxxxxxxxxxxx> · Mon, 22 May 2017 13:27:01 -0400

Sorry for posting again but I was really wondering if it is somehow possible to tune gluster in order to make better use of all my cores (see below for the details). I suspect that is the reason for the high sporadic context switches I have been experiencing.

Cheers!

-------- Original Message --------
Subject: Re: [Gluster-users] 120k context switches on GlsuterFS nodes
Local Time: May 18, 2017 8:43 PM
UTC Time: May 18, 2017 6:43 PM
From: mabi@xxxxxxxxxxxxx
To: Ravishankar N <ravishankar@xxxxxxxxxx>
Pranith Kumar Karampuri <pkarampu@xxxxxxxxxx>, Gluster Users <gluster-users@xxxxxxxxxxx>, Gluster Devel <gluster-devel@xxxxxxxxxxx>

I have a single  Intel Xeon CPU E5-2620 v3 @ 2.40GHz in each nodes and this one has 6 cores and 12 threads. I thought this would be enough for GlusterFS. When I check my CPU graphs everything is pretty much idle and there is hardly any peeks at all on the CPU. During the very high context switch my CPU graphs shows the following:

1 thread was 100% busy in CPU user
1 thread was 100% busy in CPU system

leaving actually 10 other threads out of the total of 12 threads unused...

Is there maybe any performance tuning parameters I need to configure in order to make a better use of my CPU cores or threads?

-------- Original Message --------
Subject: Re: [Gluster-users] 120k context switches on GlsuterFS nodes
Local Time: May 18, 2017 7:03 AM
UTC Time: May 18, 2017 5:03 AM
From: ravishankar@xxxxxxxxxx
To: Pranith Kumar Karampuri <pkarampu@xxxxxxxxxx>, mabi <mabi@xxxxxxxxxxxxx>
Gluster Users <gluster-users@xxxxxxxxxxx>, Gluster Devel <gluster-devel@xxxxxxxxxxx>

On 05/17/2017 11:07 PM, Pranith Kumar
      Karampuri wrote:
+ gluster-devel

On Wed, May 17, 2017 at 10:50 PM, mabi <mabi@xxxxxxxxxxxxx> wrote:

I don't know exactly what kind of context-switches it
              was but what I know is that it is the "cs" number under
              "system" when you run vmstat.
Okay, that could be due to the  syscalls themselves or pre-emptive
    multitasking in case there aren't enough cpu cores. I think the
    spike in numbers is due to more users accessing the files at the
    same time like you observed, translating into more syscalls.  You
    can try capturing the gluster volume profile info the next time it
    occurs and co-relate with the cs count. If you don't see any
    negative performance impact, I think you don't need to be bothered
    much by the numbers.

HTH,
Ravi

Also I use the percona linux monitoring template for
              cacti (https://www.percona.com/doc/percona-monitoring-plugins/LATEST/cacti/linux-templates.html)
              which monitors context switches too. If that's of any use
              interrupts where also quite high during that time with
              peaks up to 50k interrupts.

-------- Original Message --------
Subject: Re: [Gluster-users] 120k context
                    switches on GlsuterFS nodes
Local Time: May 17, 2017 2:37 AM
UTC Time: May 17, 2017 12:37 AM
From: ravishankar@xxxxxxxxxx
To: mabi <mabi@xxxxxxxxxxxxx>,
                    Gluster Users <gluster-users@xxxxxxxxxxx>

On
                    05/16/2017 11:13 PM, mabi wrote:
Today I even saw up to 400k context switches
                      for around 30 minutes on my two nodes replica...
                      Does anyone else have so high context switches on
                      their GlusterFS nodes?

I am wondering what is "normal" and if I should
                      be worried...

-------- Original Message --------
Subject: 120k context switches on GlsuterFS
                        nodes
Local Time: May 11, 2017 9:18 PM
UTC Time: May 11, 2017 7:18 PM
From: mabi@xxxxxxxxxxxxx
To: Gluster Users <gluster-users@xxxxxxxxxxx>

Hi,

Today I noticed that for around 50 minutes my
                        two GlusterFS 3.8.11 nodes had a very high
                        amount of context switches, around 120k. Usually
                        the average is more around 1k-2k. So I checked
                        what was happening and there where just more
                        users accessing (downloading) their files at the
                        same time. These are directories with typical
                        cloud files, which means files of any sizes
                        ranging from a few kB to MB and a lot of course.

Now I never saw such a high number in context
                        switches in my entire life so I wanted to ask if
                        this is normal or to be expected? I do not find
                        any signs of errors or warnings in any log
                        files.

What context switch are you referring to
                    (syscalls context-switch on the bricks?) ? How did
                    you measure this?
-Ravi

My volume is a replicated volume on two nodes
                        with ZFS as filesystem behind and the volume is
                        mounted using FUSE on the client (the cloud
                        server). On that cloud server the glusterfs
                        process was using quite a lot of system CPU but
                        that server (VM) only has 2 vCPUs so maybe I
                        should increase the number of vCPUs...

Any ideas or recommendations?

Regards,
M.

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--
Pranith

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