Due to modern technology trends, fault tolerance (FT) is acquiring an ever increasing research attention. To reduce the overhead introduced by the FT features, several techniques have been proposed. One of these techniques is Instruction-Level Fault Tolerance Configurability (ILCOFT). ILCOFT enables application developers to protect different instructions at varying degrees, devoting more resources to protect the most critical instructions, and saving resources by weakening protection of other instructions. It is, however, not trivial to assign a proper protection level for every instruction. This work introduces the notion of Instruction Vulnerability Factor (IVF), which evaluates how faults in every instruction affect the final application output. The IVF is computed off-line, and is then used by ILCOFT-enabled systems to assign the appropriate protection level to every instruction. IVF releases the programmer from the need to assign the necessary protection level to every instruction by hand. Experimental results demonstrate that IVF-based ILCOFT reduces the instruction duplication performance penalty by up to 77%, while the maximum output damage due to undetected faults does not exceed 0.6% of the total application output.

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Single-Instruction Multiple-Data (SIMD) instructions provide an inexpensive way to exploit the Data-Level Parallelism in multimedia applications. However, the performance improvement obtained by employing SIMD instructions is often limited because frequently many overhead instructions are required to bring data in a form amenable to SIMD processing. In this paper, we employ two techniques to overcome this limitation. The first technique, extended subwords, uses four extra bits for every byte in a media register. This allows many SIMD operations to be performed without overflow and avoids packing/unpacking conversion overhead. The second technique, Matrix Register File (MRF), allows flexible row-wise as well as column-wise access to the register file. It is useful for many two-dimensional multimedia algorithms such as the (I) Discrete Cosine Transform, 2 × 2 Haar Transform, and pixel padding. In addition, we propose a few new media instructions. Experimental results obtained by extending the SimpleScalar toolset show that these techniques improve performance by up to a factor of 4.5 compared to a conventional SIMD instruction set extension.

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Due to modern technology trends such as decreasing feature sizes and lower voltage levels, fault tolerance (FT) is becoming increasingly important in computing systems. Several schemes have been proposed to enable a user to configure the FT at the application level, thereby enabling the user to trade stronger FT for performance or vice versa. In this paper, we propose supporting instruction-level rather than application-level configurability of FT, since different parts of some applications (e.g., multimedia) can have different reliability requirements. Weak or no FT will be applied to less critical parts, resulting in time and/or resource gains. These gains can be used to apply stronger FT techniques to the more critical parts; hence increasing the overall reliability. The paper shows how some existing FT techniques can be adapted to support instruction-level FT configurability, how a programmer can specify the desired FT level of the instructions, and how the compiler can manage it automatically. A comparison between the existing FT scheme EDDI (which duplicates all instructions) and the proposed approach is performed both at the kernel and at full application levels. The simulation results show that both the performance and the energy consumption are significantly improved (up to 50% at the kernel and up to 16% at full application level), while the fault coverage depends on the application. For the full application (JPEG encoder), our approach is only applied to one kernel in order to avoid increasing the programming effort significantly.