Re: Oracle RAC and IRQ Balance

   NIC cards interrupt CPU for the packet delivery. Of course, in a busy RAC database, there can be huge amount of network packets being transferred leading to high IRQs. If IRQs are pinned to be interrupted to one CPU, then latency in that CPU can cause issues as kernel threads need to be scheduled to serve the irqs only in that CPU.

   If you want IRQs to be pinned to one CPU, then you should make sure that no other process is scheduled to execute in that CPU. But, I see that 40% of usage in CPU in USER mode which indicates that this is probably not happening in your case.
  But, why is this important for you? Do you see network delays causing RAC performance issues? If yes, then I don't see an issue of IRQs being serviced by all CPUs. Also, I am surprised that this is not a default. Cheers

Riyaj Shamsudeen
Principal DBA,
Ora!nternals - http://www.orainternals.com - Specialists in Performance, RAC and EBS11i
Blog: http://orainternals.wordpress.com
Oracle ACE Director and OakTable member http://www.oaktable.com

Co-author of the books: Expert Oracle
Practices<http://tinyurl.com/book-expert-oracle-practices/>, Pro Oracle SQL, Expert PL/SQL
Practices<http://tinyurl.com/book-expert-plsql-practices>

On Mon, Oct 3, 2011 at 4:29 PM, Walker, Jed S <Jed_Walker_at_cable.comcast.com>wrote:

> Back to my learning of RAC. Today, it was suggested that we turn on
> IRQBALANCE on our Oracle 11.2.0 RAC systems to help distribute the IRQ load,
> to hopefully help with performance. I did a check and can see that just one
> CPU appears to be handling all of these.
> mpstat -P ALL 2
> Linux 2.6.18-53.el5 (node-01) 10/03/2011
>
> 09:19:46 PM CPU %user %nice %sys %iowait %irq %soft %steal
> %idle intr/s
> 09:19:48 PM all 14.30 0.00 3.04 23.54 0.25 1.27 0.00
> 57.59 10903.06
> 09:19:48 PM 0 41.33 0.00 9.18 40.31 1.02 4.08 0.00
> 4.08 10902.55
> 09:19:48 PM 1 2.55 0.00 0.51 14.29 0.00 0.00 0.00
> 82.65 0.00
> 09:19:48 PM 2 12.24 0.00 2.04 34.18 0.00 0.00 0.00
> 52.04 0.00
> 09:19:48 PM 3 1.02 0.00 0.51 6.63 0.00 0.00 0.00
> 92.35 0.00
> (this is consistent over a period of time)
>
> I then read an article saying that in many cases this doesn't matter -
> something to do with processes being pinned to a CPU (Sorry, I can't find
> the article again!).
>
> Does anyone have any experience, or is there a good practice for this and
> RAC?
>
> service irqbalance start
> chkconfig irqbalance on
>
> Thanks,
>
> Jed
>
>
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>
>
>

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