IBM Power11 processors incorporate spare cores as an advanced error handling mechanism to ensure system reliability and to minimize the downtime. This blog explains the importance of spare cores in modern processor design, focusing on IBM Power11 implementation. It details how a spare core ensures system reliability, minimizes downtime, and maintains performance by taking over faulty cores' functions. The blog covers spare core management, advantages, and functionality, emphasizing its role in robust fault handling and high availability.

Overview of spare core

In modern processor design, having one spare core per processor is crucial for maintaining system reliability and minimizing downtime. A spare core in Power11 is an additional processor core within a multi-core chip that can take over the functions of a faulty or malfunctioning core. This redundancy ensures that the system can continue operating even when a core fails, preventing downtime and maintaining performance. Spare cores are typically managed by the processor's hardware and firmware, which monitor core health and dynamically replace faulty cores with spare ones, both during runtime and during the system boot time. This process helps minimize system disruptions and reduces the need for planned outages to repair bad cores. Currently, one spare core is supported on a Power11 processor chip.

The service processor shows all the cores including the spare core along with their functional state. The spare core remains hidden from the partition and the Hardware Management Console (HMC), ensuring seamless operation without additional licensing costs. The system firmware passes all the resource information including spare core information to IBM Power Hypervisor which takes care of excluding spare core to be assigned to the partitions. During the fault on a core assigned to a partition, Power Hypervisor will take action to replace the bad core with the spare core.

Advantages of Power11 spare core support for robust system design:

• Increased system reliability: Spare cores enable the system to continue operating even when a core fails, minimizing downtime and ensuring high availability.
• Reduced maintenance: By automatically replacing faulty cores with spare ones, spare cores help reduce the need for manual intervention and maintenance.
• Improved fault tolerance:Spare cores enhance fault tolerance by allowing the system to isolate and replace bad cores without causing a complete system crash.

Power11 spare core: A key enabler for robust fault handling

Following are comprehensive details on the handling of different core error scenarios, with specific emphasis on mechanisms involving spare core availability:

• When a predictive error reaches a certain threshold, the affected core is made inoperable by the Power Hypervisor, which then replaces the affected core with the spare core at runtime. This dynamic replacement process helps prevent system crashes, degraded system performance and eliminates the need for planned outages to fix bad cores.

• When a local core checkstop occurs, the faulty core stops executing instructions and the spare core automatically takes over the functions of the problematic core, ensuring that the system performance remains unaffected. This mechanism helps maintain system stability and reliability in the presence of core-level faults.

  Note: A checkstop is a hardware-detected error that causes a processor core to stop executing instructions. Checkstops are logged and may trigger system recovery mechanisms, such as replacing the faulty core with a spare core in systems with spare core support.

• For errors leading to a system checkstop, the system opts for re-IPL (reboot), de-configuring the fatal-guarded core. It marks the fatal-guarded core as spare-guarded. The system then replaces it with the available spare core and completes the re-IPL.

  Note:

  • IPL (initial program load) refers to the process of loading an operating system or firmware into a system's memory during boot-up.
  • A fatal-guarded core is a processor core that has been identified as potentially faulty or malfunctioning. The system monitors these cores and may replace them with spare cores during operation or reboot to maintain system stability and reliability.
• If another core on the same processor encounters an error, the customer experiences a reduced number of cores. Once a spare core is deployed, the error behavior is same as before and in such a case, the Product Engineer (PE) needs to replace the processor chip.
• When the first core is errored on a processor, it is marked as spare-guarded, and the spare core is allocated in place of the errored core. Errors associated with the initial fault that deploys the spare are logged as informational events. When the next fault on a processor core occurs, the errors are logged as normal.

These benefits contribute to more robust, reliable, and efficient systems, ultimately improving the user experience and reducing maintenance costs.

Conclusion

Spare cores in Power11 processors are self-managed, meaning users do not need to manually configure or monitor them. The system automatically manages spare cores to compensate for faults in functional cores, ensuring continuous operation and performance without manual intervention.