System Administration Guide

What's New in System Performance

This section describes new system performance features in the Solaris 2.6 release.

Scheduler Activation

Scheduler activations provide kernel scheduling support for applications with particular scheduling needs, such as database and multithreaded applications. Multithreaded support changes for scheduler activation are implemented as a private interface between the kernel and the libthread library, without changing the libthread interface. Additionally, applications may give scheduling hints to the kernel to improve performance. See libsched(3X) for more information.

The `psrset` Command

Another new feature allows a group of processors to be allocated for the exclusive use of one or more applications. The /usr/sbin/psrset command gives a system administrator control over the creation and management of processor sets. See psrset(1M) for more information.

UFS Direct Input/Output (I/O)

Direct I/O is intended to boost bulk I/O operations. Bulk I/O operations use large buffer sizes to transfer large files (files larger than physical memory).

An example of a bulk I/O operation is downloading satellite data, which writes large amounts of data to a file. Direct I/O data is read or written into memory without using the overhead of the operating system's page caching mechanism.

There is a potential penalty on direct I/O startup. If a file requested for I/O is already mapped by another application, the pages will have to be flushed out of memory before the direct I/O operation can begin.

See directio(3C) for more information.

Direct I/O can also be enabled on a file system by using the forcedirectio option to the mount command. Enabling direct I/O is a performance benefit only when a file system is transferring large amounts of sequential data.

When a file system is mounted with this option, data is transferred directly between a user's address space and the disk. When forced direct I/O is not enabled for a file system, data transferred between a user's address space and the disk is first buffered in the kernel address space.

The default behavior is no forced direct I/O on a UFS file system. See mount_ufs for more information.

How to Enable Forced Direct I/O on a UFS File System

Become superuser.

Mount a file system with the forcedirectio mount option.

# mount -F ufs -o forcedirectio /dev/dsk/c0t3d0s7 /datab

Verify the mounted file system has forced direct I/O enabled.

# mount
                    .
                    .
                    .
/export/home on /dev/dsk/c0t3d0s7 forcedirectio/setuid/read/write/largefiles
on Mon May 12 13:47:55 1997

Enhancements to the `/proc` File System and Watchpoints

The previous flat /proc file system has been restructured into a directory hierarchy that contains additional sub-directories for state information and control functions.

It also provides a watchpoint facility that is used to remap read/write permissions on the individual pages of a process's address space. This facility has no restrictions and is MT-safe.

The new /proc file structure provides complete binary compatibility with the old /proc interface except that the new watchpoint facility cannot be used with the old interface.

Debugging tools have been modified to use /proc's new watchpoint facility, which means the entire watchpoint process is faster.

The following restrictions have been removed when setting watchpoints using the dbx debugging tool:

Setting watchpoints on local variables on the stack due to SPARC register windows
Setting watchpoints on multi-threaded processes

See proc(4), core(4), adb(4) for more information.