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Old 07-12-2012, 11:00 AM
Suvayu Ali
 
Default How to debug high system load?

Hi,

I have a ThinkPad (Core i7, 2.67GHz) with F17 and I'm seeing high system
loads persistently. Right from boot up I see loads of 1, and often it
goes up to 2 or more.

Things I have looked at:
1. I'm using Xfce, so the desktop environment is also light.
2. I looked at the output of `systemctl list-units' and don't see any
unnecessary services enabled.
3. top only says currently Xorg is the most active process with 1% CPU
activity. From the activity summary of atop since boot, I see it's
Xorg with 3% CPU usage. And while idling all my 4 logical cores are
throttled down and are at about 1%.

So my question is since CPU usage is already so low, what could be
driving up the system load? This is bugging me since I also see a
general sluggishness compared to a much faster system early this year.

Thanks for any ideas.

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Old 07-12-2012, 01:29 PM
Andrew Haley
 
Default How to debug high system load?

On 07/12/2012 12:00 PM, Suvayu Ali wrote:
> So my question is since CPU usage is already so low, what could be
> driving up the system load? This is bugging me since I also see a
> general sluggishness compared to a much faster system early this year.

top should show you. How much time in idle and wait states?

Andrew.
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Old 07-12-2012, 01:36 PM
Steven Stern
 
Default How to debug high system load?

On 07/12/2012 06:00 AM, Suvayu Ali wrote:
rottled down and are at about 1%.
>
> So my question is since CPU usage is already so low, what could be
> driving up the system load? This is bugging me since I also see a
> general sluggishness compared to a much faster system early this year.
>
> Thanks for any ideas.
>

Are you listening to music? Doing background uploads or downloads?

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Old 07-12-2012, 02:02 PM
Suvayu Ali
 
Default How to debug high system load?

On Thu, Jul 12, 2012 at 02:29:54PM +0100, Andrew Haley wrote:
> On 07/12/2012 12:00 PM, Suvayu Ali wrote:
> > So my question is since CPU usage is already so low, what could be
> > driving up the system load? This is bugging me since I also see a
> > general sluggishness compared to a much faster system early this year.
>
> top should show you. How much time in idle and wait states?
>

They are as I would expect, large idle times, and almost no wait time:

top - 15:59:42 up 3:24, 6 users, load average: 0.74, 0.87, 0.95
Tasks: 257 total, 1 running, 254 sleeping, 1 stopped, 1 zombie
Cpu0: 2.6%us, 4.0%sy, 0.0%ni, 92.7%id, 0.0%wa, 0.7%hi, 0.0%si, 0.0%st
Cpu1: 1.0%us, 0.3%sy, 0.0%ni, 98.0%id, 0.0%wa, 0.3%hi, 0.3%si, 0.0%st
Cpu2: 4.3%us, 4.3%sy, 0.0%ni, 91.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu3: 0.3%us, 0.0%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 3843356k total, 3471700k used, 371656k free, 206600k buffers
Swap: 6029308k total, 0k used, 6029308k free, 1209176k cached

> Andrew.

Thanks,

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Old 07-12-2012, 02:09 PM
Suvayu Ali
 
Default How to debug high system load?

On Thu, Jul 12, 2012 at 08:36:31AM -0500, Steven Stern wrote:
> On 07/12/2012 06:00 AM, Suvayu Ali wrote:
> rottled down and are at about 1%.
> >
> > So my question is since CPU usage is already so low, what could be
> > driving up the system load? This is bugging me since I also see a
> > general sluggishness compared to a much faster system early this year.
> >
> > Thanks for any ideas.
> >
>
> Are you listening to music? Doing background uploads or downloads?
>

No nothing like that. On login, I start two processes `conky -D' and
`emacs --daemon'. Apart from this I only have a few terminals, Firefox
and a few emacs frames open. The Xfce session amanger starts pidgin and
dropbox. That's about all the processes.

I also use OfflineIMAP to sync my email, but that is setup to run every
5 minutes, and it has been setup as a cron job for ages; I never had
problems with it before.

Right now, my network usage is less than a KiB/s, both upload and
download, and my lod average is 0.98!

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Old 07-12-2012, 02:12 PM
Andrew Haley
 
Default How to debug high system load?

On 07/12/2012 03:02 PM, Suvayu Ali wrote:
> On Thu, Jul 12, 2012 at 02:29:54PM +0100, Andrew Haley wrote:
>> On 07/12/2012 12:00 PM, Suvayu Ali wrote:
>>> So my question is since CPU usage is already so low, what could be
>>> driving up the system load? This is bugging me since I also see a
>>> general sluggishness compared to a much faster system early this year.
>>
>> top should show you. How much time in idle and wait states?
>>
>
> They are as I would expect, large idle times, and almost no wait time:
>
> top - 15:59:42 up 3:24, 6 users, load average: 0.74, 0.87, 0.95
> Tasks: 257 total, 1 running, 254 sleeping, 1 stopped, 1 zombie
> Cpu0: 2.6%us, 4.0%sy, 0.0%ni, 92.7%id, 0.0%wa, 0.7%hi, 0.0%si, 0.0%st
> Cpu1: 1.0%us, 0.3%sy, 0.0%ni, 98.0%id, 0.0%wa, 0.3%hi, 0.3%si, 0.0%st
> Cpu2: 4.3%us, 4.3%sy, 0.0%ni, 91.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> Cpu3: 0.3%us, 0.0%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> Mem: 3843356k total, 3471700k used, 371656k free, 206600k buffers
> Swap: 6029308k total, 0k used, 6029308k free, 1209176k cached

That's very odd. Processes in 'D' = uninterruptible sleep ?

Andrew.

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Old 07-12-2012, 02:17 PM
"Bryn M. Reeves"
 
Default How to debug high system load?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 07/12/2012 02:36 PM, Steven Stern wrote:
> On 07/12/2012 06:00 AM, Suvayu Ali wrote: rottled down and are at
> about 1%.
>>
>> So my question is since CPU usage is already so low, what could
>> be driving up the system load? This is bugging me since I also
>> see a general sluggishness compared to a much faster system early
>> this year.
>>
>> Thanks for any ideas.
>>
>
> Are you listening to music? Doing background uploads or
> downloads?
>

That would normally also be reflected to some extent in CPU usage and
process activity as shown in top (unless the problem was buffering
them from a really slow network file system or something).

I would think Andrew is correct - the load is most likely being driven
up by processes that are waiting on I/O (D-state, aka uninterruptible
sleep).

On Linux the load average represents the 1m, 5m and 15m decaying
average of the number of processes that are either runnable (waiting
on a runqueue or actually executing on the CPU) /and/ the number of
processes blocked on I/O.

There's a fair bit of inaccurate information about the definition of
the load average on Linux floating around - this comes from the fact
that it's calculated slightly differently on the Sys V UNIXes and BSD
vs. Linux. Traditionally only the runqueue length (tasks running or
waiting to be scheduled) are counted as "active".

On Linux the "number of active processes" includes both tasks on the
runqueue and tasks blocked on I/O; this means it's hard to compare the
numbers meaningfully between BSD/Solaris and Linux even when running
on the same hardware.

Even well-known Linux magazines have managed to print entire articles
that got this completely wrong in the past..

Regards,
Bryn.
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Old 07-12-2012, 02:24 PM
Suvayu Ali
 
Default How to debug high system load?

On Thu, Jul 12, 2012 at 03:12:00PM +0100, Andrew Haley wrote:
> On 07/12/2012 03:02 PM, Suvayu Ali wrote:
> > On Thu, Jul 12, 2012 at 02:29:54PM +0100, Andrew Haley wrote:
> >> On 07/12/2012 12:00 PM, Suvayu Ali wrote:
> >>> So my question is since CPU usage is already so low, what could be
> >>> driving up the system load? This is bugging me since I also see a
> >>> general sluggishness compared to a much faster system early this year.
> >>
> >> top should show you. How much time in idle and wait states?
> >>
> >
> > They are as I would expect, large idle times, and almost no wait time:
> >
> > top - 15:59:42 up 3:24, 6 users, load average: 0.74, 0.87, 0.95
> > Tasks: 257 total, 1 running, 254 sleeping, 1 stopped, 1 zombie
> > Cpu0: 2.6%us, 4.0%sy, 0.0%ni, 92.7%id, 0.0%wa, 0.7%hi, 0.0%si, 0.0%st
> > Cpu1: 1.0%us, 0.3%sy, 0.0%ni, 98.0%id, 0.0%wa, 0.3%hi, 0.3%si, 0.0%st
> > Cpu2: 4.3%us, 4.3%sy, 0.0%ni, 91.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> > Cpu3: 0.3%us, 0.0%sy, 0.0%ni, 99.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
> > Mem: 3843356k total, 3471700k used, 371656k free, 206600k buffers
> > Swap: 6029308k total, 0k used, 6029308k free, 1209176k cached
>
> That's very odd. Processes in 'D' = uninterruptible sleep ?
>

I looked through the entire process list all but 3 were "sleeping", 2
were stopped (I did that in a terminal, a less instance and an
emacsclient instance) and one was zombie (again I know this one, it's
the src-hilite attached to the stopped less instance).

> Andrew.
>

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Old 07-12-2012, 02:29 PM
Suvayu Ali
 
Default How to debug high system load?

Hi Bryn,

On Thu, Jul 12, 2012 at 03:17:01PM +0100, Bryn M. Reeves wrote:
>
> That would normally also be reflected to some extent in CPU usage and
> process activity as shown in top (unless the problem was buffering
> them from a really slow network file system or something).
>

I do have AFS (authenticated with Kerberos) on my laptop, although I'm
not using it at the moment. There are no background jobs that should
access it either. Only time AFS is used is when I explicitly run some
jobs (through python scripts) for my research.

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Old 07-12-2012, 02:34 PM
"Bryn M. Reeves"
 
Default How to debug high system load?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 07/12/2012 03:29 PM, Suvayu Ali wrote:
> Hi Bryn,
>
> On Thu, Jul 12, 2012 at 03:17:01PM +0100, Bryn M. Reeves wrote:
>>
>> That would normally also be reflected to some extent in CPU usage
>> and process activity as shown in top (unless the problem was
>> buffering them from a really slow network file system or
>> something).
>>
>
> I do have AFS (authenticated with Kerberos) on my laptop, although
> I'm not using it at the moment. There are no background jobs that
> should access it either. Only time AFS is used is when I explicitly
> run some jobs (through python scripts) for my research.
>

Hi Suvayu,

It's possible that you have processes spending brief periods in
D-state - short enough that they are hard to spot in top with the
default sample period but long enough to count toward the load average
(it's possible there's some other explanation though but that's what
I'd try to rule out first).

You could use tools like blktrace, iotop and latencytop to try to
investigate further or if you're willing to install systemtap you
could use the "sleepingBeauties.stp" script to look for processes
spending >10ms in this state (and dump their stacks when they do).

Regards,
Bryn.

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