6.3 Solaris OS Tuning Features

Starting with the Solaris 9 release, the operating system provides scalability and high performance for the SunFire^TM systems. New features introduced with Solaris 9 OS that improve the performance of OpenMP programs without hardware upgrades are Memory Placement Optimizations (MPO) and Multiple Page Size Support (MPSS), among others.

MPO allows the OS to allocate pages close to the processors that access those pages. SunFire E20K, and SunFire E25K systems have different memory latencies within the same UniBoard^TM versus between different UniBoards. The default MPO policy, called first-touch, allocates memory on the UniBoard containing the processor that first touches the memory. The first-touch policy can greatly improve the performance of applications where data accesses are made mostly to the memory local to each processor with first-touch placement. Compared to a random memory placement policy where the memory is evenly distributed throughout the system, the memory latencies for applications can be lowered and the bandwidth increased, leading to higher performance.

The MPSS feature is supported as of the Solaris 9 OS release, and allows a program to use different page sizes for different regions of virtual memory. The default Solaris page size is relatively small (8KB on UltraSPARC processors and 4KB on AMD64 Opteron processors). Applications that suffer from too many TLB misses may experience a performance boost by using a larger page size.

TLB misses can be measured using the Sun Performance Analyzer.

The default page size on a specific platform can be obtained with the Solaris OS command: /usr/bin/pagesize . The -a option on this command lists all the supported page sizes. (See the pagesize(1) man page for details.)

There are three ways to change the default page size for an application:

• Use the Solaris OS command ppgsz(1)

• Compile the application with the -xpagesize, -xpagesize_heap, and -xpagesize_stack options. (See the compiler man pages for details.)

• Use MPSS specific environment variables. See the mpss.so.1(1) man page for details.