Performance Issue with CPU Processing In Exalogic X4-2 Virtual Racks

Asset ID:	1-72-1925546.1
Update Date:	2015-08-08
Keywords:

Solution Type Problem Resolution Sure

Solution 1925546.1 : Performance Issue with CPU Processing In Exalogic X4-2 Virtual Racks

Applies to:

Exalogic Elastic Cloud X4-2 Hardware - Version X4 to X4 [Release X4]
Linux x86-64
Oracle Virtual Server (x8-64)

Symptoms

In Exalogic X4-2 racks running Virtual releases 2.0.6.x, in few of the compute nodes performance issues with CPU processing speeds is observed.

This issue can be verified using following commands:

dmidecode -t processor | grep "Speed"

cat /var/log/dmesg | grep "MHz processor"

cat /proc/cpuinfo | grep "MHz"

time echo "scale=10000; 4*a(1)" | bc -l

Above command outputs shows CPU processing speed in MHz. Below is sample output for reference

Max Speed: 2933 MHz
Current Speed: 2933 MHz

On the problematic nodes we see the CPU processing speeds are varying more than 10 seconds when compared to nodes which do not have issues.

Cause

This issue happens due misconfiguration of CPU speed scaling.

To verify this we can check inside file:

/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor

In above file cpu* is CPU number for e.g. cpu0, cpu1 etc.

Following is the snippet of the node which had problem.

# cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
GOVERNOR=ondemand

From above output we see that the GOVERNOR value is set as "ondemand". The recommended value for it is "performance".

NOTE:
Please note that the CPU processing on each node may vary depending on the memory used, caching, I/O load, specific applications used on that Node. So a Node which is having load with memory intrusive apps and high IO may be having slightly lower CPU processing speeds.

Solution

Follow belows steps to fix this issue:

Edit "/etc/sysconfig/cpuspeed" file

Change

GOVERNOR=ondemand

To

GOVERNOR=performance
Run following command after the change

service cpuspeed restart

Below is sameple snippet of above command.

Disabling ondemand cpu frequency scaling: [ OK ]
Enabling performance cpu frequency scaling: [ OK ]
Verify if the settings are applied correctly as follows:

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
performance

Above command should be showing "performance" as the output.

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