Huge leaps in performance and power improvements of computing systems are driven by rapid technology scaling, but technology scaling has also rendered computing systems susceptible to soft errors. Among the soft error protection techniques, Control Flow Checking (CFC) based techniques have gained a reputation of being lightweight yet effective. The main idea behind CFCs is to check if the program is executing the instructions in the right order. In order to validate the protection claims of existing CFCs, we develop a systematic and quantitative method to evaluate the protection achieved by CFCs using the metric of vulnerability. Our quantitative analysis indicates that existing CFC techniques are not only ineffective in providing protection from soft faults, but incur additional performance and power overheads. Our results show that software-only CFC protection schemes increase system vulnerability by 18%--21% with 17%--38% performance overhead and hybrid CFC protection increases vulnerability by 5%. Although the vulnerability remains almost the same for hardware-only CFC protection, they incur overheads of design cost, area, and power due to the hardware modifications required for their implementations.

Control Flow Checking (CFC) based techniques have gained a reputation of providing effective, yet low-overhead protection from soft errors. The basic idea is that if the control flow -- or the sequence of instructions that are executed -- is correct, then most probably the execution of the program is correct. Although researchers claim the effectiveness of the proposed CFC techniques, we argue that their evaluation has been inadequate and can even be wrong! Recently, the metric of vulnerability has been proposed to quantify the susceptibility of computation to soft errors. Laced with this comprehensive metric, we quantitatively evaluate the effectiveness of several existing CFC schemes, and obtain surprising results. Our results show that existing CFC techniques are not only ineffective in protecting computation from soft errors, but that they incur additional power and performance overheads. Software-only CFC protection schemes (CFCSS [14], CFCSS+NA [2], and CEDA [18]) increase system vulnerability by 18% to 21% with 17% to 38% performance overhead; Hybrid CFC protection technique, CFEDC [4] also increases the vulnerability by 5%; While the vulnerability remains almost the same for hardware only CFC protection technique, CFCET [15], they cause overheads of design cost, area, and power due to the hardware modifications required for their implementations.

Reducing device dimensions, increasing transistor densities, and smaller timing windows, expose the vulnerability of processors to soft errors induced by charge carrying particles. Since these factors are only consequences of the inevitable advancement in processor technology, the industry has been forced to improve reliability on general purpose chip multiprocessors (CMPs). With the availability of increased hardware resources, redundancy-based techniques are the most promising methods to eradicate soft-error failures in CMP systems. In this work, we propose a novel customizable and redundant CMP architecture (UnSync) that utilizes hardware-based detection mechanisms (most of which are readily available in the processor), to reduce overheads during error-free executions. In the presence of errors (which are infrequent), the always forward execution enabled recovery mechanism provides for resilience in the system. The inherent nature of our architecture framework supports customization of the redundancy, and thereby provides means to achieve possible performance-reliability tradeoffs in many-core systems. We provide a redundancy-based soft-error resilient CMP architecture for both write-through and write-back cache configurations. We design a detailed RTL model of our UnSync architecture and perform hardware synthesis to compare the hardware (power/area) overheads incurred. We compare the same with those of the Reunion technique, a state-of-the-art redundant multicore architecture. We also perform cycle-accurate simulations over a wide range of SPEC2000, and MiBench benchmarks to evaluate the performance efficiency achieved over that of the Reunion architecture. Experimental results show that, our UnSync architecture reduces power consumption by 34.5 percent and improves performance by up to 20 percent with 13.3 percent less area overhead, when compared to the Reunion architecture for the same level of reliability achieved.

Reducing device dimensions, increasing transistor densities, and smaller timing windows, expose the vulnerability of processors to soft errors induced by charge carrying particles. Since these factors are only consequences of the inevitable advancement in processor technology, the industry has been forced to improve reliability on general purpose Chip Multiprocessors (CMPs). With the availability of increased hardware resources, redundancy based techniques are the most promising methods to eradicate soft error failures in CMP systems. In this work, we propose a novel redundant CMP architecture (UnSync) that utilizes hardware based detection mechanisms (most of which are readily available in the processor), to reduce overheads during error free executions. In the presence of errors (which are infrequent), the "always forward execution" enabled recovery mechanism provides for resilience in the system. We design a detailed RTL model of our UnSync architecture and perform hardware synthesis to compare the hardware (power/area) overheads incurred. We compare the same with those of the Reunion technique, a state-of-the-art redundant multi-core architecture. We also perform cycle-accurate simulations over a wide range of SPEC2000, and MiBench benchmarks to evaluate the performance efficiency achieved over that of the Reunion architecture. Experimental results show that, our UnSync architecture reduces power consumption by 34.5% and improves performance by up to 20% with 13.3% less area overhead, when compared to Reunion architecture for the same level of reliability achieved.