IBM 6.1.X manual POWER5

J V M H E A P L A R G E P A G E

Large pages can reduce the CPU overhead needed to keep track of heap. With this setting we have seen 10% throughput improvement in our measurements.

This setting does improve performance on Windows, we did not set it for our measurements because Portal doesn’t start reliably when –Xlp is set, sometimes it requires a system reboot to get the jvm to start.

How-to Set: In the WebSphere Administrative Console: Servers -> Application Servers ->

WebSphere Portal -> Server Infrastructure: Java and Process Management -> Process Definition -> Java Virtual Machine -> Generic JVM Argument. Add –Xlp .

Large pages are supported by systems running Linux kernels V2.6 or higher. See JVM Large Page Tuning for AIX Operation System.

J V M L A R G E P A G E T U N I N G O N A I X O P E R A T I N G S Y S T E M

To use JVM Large Page, AIX operating system must be configured to support large pages.

How-To Set:

1.We use the following steps to allocate 4GB of RAM as large pages (16MB) . We chose this amount based on having 8GB of physical memory in these systems. These values may need to be adjusted on systems with different amounts of physical memory.

vmo -r -o lgpg_regions=256 -o lgpg_size=16777216 bosboot -ad /dev/ipldevice

reboot -q

vmo -p -o v_pinshm=1

chuser capabilities=CAP_BYPASS_RAC_VMM,CAP_PROPAGATE $USER

2.Add: -Xlp command-line option as described above.

3.In the WebSphere Administrative Console: Servers ￿ Application Servers ￿

WebSphere Portal ￿ Server Infrastructure: Java and Process Management￿Process

Definition-> Environment Entries ￿ New ￿ EXTSHM=OFF (note: When EXTSHM is on it prevents use of large page).

4.Restart Portal Server. To verify if large pages are being used, run the AIX command vmstat -l 1 5 and check the "alp" column which is the active large page used. It should be a non-zero value if large pages are being used.

Parameter	AIX	Linux	Solaris	Windows	z/Linux	z/OS
	POWER5			2003
JVM Heap	-Xlp	-Xlp	Not	Not	Not	Not
Large page			Applicable	Applicable	Applicable	Applicable

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W E BS P HE R E P O R T AL V 6 . 1 T U N I N G G U I D E