Comments on: Understanding Linux Load Average – Part 3

By: Maurilio

Maurilio — Sat, 18 May 2013 15:01:01 +0000

Congratulations, it´s a great explanation of load average. Now all clear for me.

Thanks a lot.

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[...] 2. Understanding Linux Load Average 谢谢 @jametong 参考：part1 part2 part3 [...]

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[...] Understanding Linux Load Average – Part 3 [...]

By: Stefan

Stefan — Sun, 21 Oct 2012 15:02:09 +0000

Hi Harald,

you already have demonstrated the behaviour. The uninterruptable state is used for a short term wait and disk I/O falls into this category. Look for the section “process state codes” in the manpage for “ps” and you will find the state “D” for “Uninterruptible sleep (usually IO)”. And surely you have seen LGWR or other I/O intensive processes in this state. So this has already been part of your analysis.

Regards,
Stefan

By: Harald van Breederode

Harald van Breederode — Fri, 05 Oct 2012 12:34:32 +0000

Hi Adrian,

Thanx for your comment. I didn’t know that. Can you give examples when a process enters a uninterruptable sleep state? (It was long ago that I knew exactly what is going on in the kernel ;-) Maybe I am able to demonstrate this behaviour.
-Harald

By: Adrian

Adrian — Thu, 04 Oct 2012 22:24:41 +0000

Hello Harald,

very good article.

Just one interesting note.
In “Load Average” on Linux are also processes in uninterruptible sleep states. So high Load Average on Linux does not always reflect CPU or I/O activity.

Adrian

By: luciano

luciano — Fri, 24 Aug 2012 09:11:47 +0000

Excellent article.

I have just one comment about: In the third part it says: “The above output also reveals that the high CPU utilization is mainly caused by handling software interrupts, 52% in this case.

“, acording to mpstat manual, system cpu time doesn’t take soft or hard interruptions into account.

By: siva

siva — Wed, 22 Aug 2012 17:20:39 +0000

Hi ,

Excellent atricle.Could you please share load-gen scripts .

siva

By: jason smith

jason smith — Sun, 17 Jun 2012 17:22:49 +0000

“…because it is a way more optimized kernel.” – that’s exactly our explanation :)

but yeah are load averages w/ UEK are significantly lower. I’ve run w/ the RHEL kernel and made hot /proc changes to say the cpu scheduler and io scheduler that Oracle defaults to and see differences in system behavior.

By: Harald van Breederode

Harald van Breederode — Sun, 17 Jun 2012 13:01:06 +0000

Hi Jason,

No, I haven’t looked at the differences between the stock and UEK kernels. I doubt there is a change in how the load averages are calculated. I think the UEK reports lower load averages simply because it is a way more optimized kernel.
-Harald

By: jason smith

jason smith — Fri, 15 Jun 2012 05:41:11 +0000

Good stuff.

I see you’re using the UEK kernel. I’m particularly trying to find out why the UEK kernel shows better Load Averages than it’s RHEL counterpart. If you install Oracle Linux you get both kernels; and in 6 even the RHEL kernel performs better than back in 5. However, at least in our production systems – the UEK kernel reports much lower load averages.

Have you done any testing or know exactly why the UEK kernel shows better load average numbers vs the RHEL stock kernels?

Thanks,

By: Harald van Breederode

Harald van Breederode — Fri, 08 Jun 2012 09:07:50 +0000

Hi Frits,

Thanx for youe
-Harald

By: Frits Hoogland

Frits Hoogland — Thu, 07 Jun 2012 14:23:07 +0000

Harald, you might want to add ‘sar’ is in the ‘sysstat’ package. Upon installation (using the sysstat rpm package on linux), sar collects data per 10 minutes (via the configuration file /etc/cron.d/sysstat). This data is stored in /var/log/sa.

By: Harald van Breederode

Harald van Breederode — Wed, 30 May 2012 13:28:05 +0000

Thank you Kris.
-Harald

By: Harald van Breederode

Harald van Breederode — Wed, 30 May 2012 13:23:55 +0000

Hi Narendra,

Thanx for your positive comment.
Feel free to send me an email to request the load-gen scripts I used.
-Harald