SUSE Linux Enterprise Real Time Extension

System Requirements

Although SUSE® Linux Enterprise Real Time Extension may be run on single processor systems, it delivers maximum benefits on multiprocessor systems. The minimum, and recommended system requirements are as follows:

Minimum System Requirements

• 512 MB physical RAM
• 5 GB available disk space

Recommended System Requirements

• Multicore / Multiprocessor system
• 1 GB physical RAM
• 10 GB available disk space

Supported Processors

• x86
• AMD64
• Intel EM64T

SUSE Linux Enterprise Real Time Extension is an add-on, and requires that SUSE Linux Enterprise Server be installed prior to adding it:

Minimum Software Requirements

• SUSE Linux Enterprise Server 10 SP2

Technical Features

SUSE Linux Enterprise Real Time Extension is based on the 2.6.22 Linux kernel, and includes the open source community's latest real time patch set–preempt_RT–a set of patches that support preemption with sleeping spinlocks, thread run interrupts, and priority inheritance. It also includes support for CPU shielding, resource assignment, and high resolution timers. Service Pack 2 adds further support for adaptive locking, the Precision Time Protocol, and includes the latest open source RDMA software stack available from the OpenFabrics Alliance, OpenFabrics Enterprise Distribution (OFED) 1.3. With Service Pack 2, Novell becomes the first Linux distributor to support customers using OFED 1.3.

Sleeping spinlocks: SUSE Linux Enterprise Real Time Extension contains modifications that make previously uninterruptible sections of the general purpose Linux operating system kernel interruptible, or preemptible. Latency is minimized, and response times are more predictable, if you can eliminate the likelihood of an uninterruptible operating system process interrupting your high priority process, or preventing it from starting. One specific modification is the sleeping spinlock. Spinlocks are one mechanism for ensuring synchronized access to system resources. Execution threads "spin" and use CPU resources, while they periodically check and wait for a lock to be released so that they can complete. The spinlocks have been modified so that they can be put to sleep, or suspended, so that they release the resources that they are holding in order for higher priority processes to be executed.

Thread run interrupts: Another specific modification that was made to make the Real Time Extension's kernel more preemptible, are kernel run interrupt threads. Interrupts are processes that are either initiated by hardware (hard interrupt) or software (soft interrupt), that once initiated, cause the Linux kernel to switch from process mode into interrupt mode. Processes running in interrupt mode in a general purpose operating system are not preemptible. With SUSE Linux Enterprise Real Time Extension, these interrupts have been bounded or encapsulated by kernel threads, and these kernel threads, which are interruptible, in turn allow the hard and soft interrupts to be preempted by user defined higher priority processes.

Priority inheritance: Priority inheritance refers to the ability of a lower priority process to assume a higher priority, if there is a higher priority process that requires the lower priority process to finish before it can accomplish its task. With SUSE Linux Enterprise Real Time Extension, kernel services invoked by a high priority process will not wait indefinitely while other kernel services invoked by a low priority process holding a required semaphore trudge along at that lower priority. The priority of the lower priority process will be increased, or will inherit that of the higher priority, until its semaphore is released. Also, the Real Time Extension offers an alternate glibc which extends priority inheritance to user space. Applications using this alternative glibc can request that priority inheritance to be applied to their POSIX mutexes.

CPU shielding and assignment: With SUSE Linux Enterprise Real Time Extension, users have full control over the assignment of processes and threads to CPU's. Processes with real time requirements can be assigned to run exclusively on dedicated CPU's or cores. CPU's executing real time tasks can be completely shielded from any other processes that have not been explicitly assigned to them, ensuring that resources are always available for high priority processes, and minimally affected by increased system loads, ensuring greater reliability and predictability.

High resolution timers: The low resolution (40 millisecond) posix timer kernel services in the Real Time Extension have been replaced by a new implementation with resolution of about 2 microseconds. The amount of time the system spends processing interrupts, system calls, kernel daemons, and user applications is now accounted for at nanosecond resolution.

Features added with Service Pack 2:

Adaptive locking: The spinlocks in SUSE Linux Enterprise Real Time Extension 10 Service Pack 2 have been further modified to reduce operating system context switching times, dramatically improving the performance of throughput sensitive workloads. A new adaptive locking algorithm for kernel locks allows tasks to wait in a preemptible manner, instead of immediately releasing the CPU when waiting on a contended resource. This effectively decreases the number of context switches on the system, increasing throughput while simultaneously decreasing latency for certain applications.

Precision time protocol: SUSE Linux Enterprise Real Time Extension 10 Service Pack 2 supports the Precision Time Protocol (PTP) version 1, a time transfer protocol standard that allows the precise synchronization of high speed networks. PTP provides accuracy in the nanosecond range, and significantly improves the precision of time keeping and process accounting, compared to general purpose operating system protocols like NTP and GPS.

OFED 1.3: SUSE Linux Enterprise Real Time Extension 10 Service Pack 2 also includes OpenFabrics Enterprise Distribution (OFED) 1.3, the latest open source RDMA software stack available from the OpenFabrics Alliance, enabling the implementation of unified high speed interconnects based on InfiniBand and 10-Gigabit Ethernet. With Service Pack 2, Novell becomes the first Linux distributor to support customers using OFED 1.3.