Strlcpy and how CPUs can defy common sense
The article compares the performance of `strlcpy` in OpenBSD and glibc, revealing glibc's faster execution despite double traversal, emphasizing instruction-level parallelism and advocating for sized strings for efficiency.
Read original article
The article discusses the performance of the `strlcpy` function, particularly comparing implementations in OpenBSD and glibc. It highlights a common misconception that `strlcpy` traverses the source string only once when it fits into the destination buffer. In reality, glibc's implementation first calculates the string length using `strlen`, leading to two traversals. Benchmark tests reveal that glibc's optimized version is significantly faster than OpenBSD's, even with the double traversal. The author emphasizes the importance of instruction-level parallelism (ILP) and how dependencies in code can affect performance. The article concludes that understanding the nuances of CPU behavior is crucial for optimizing performance, as common assumptions about efficiency may not hold true in practice. The author also advocates for using sized strings instead of null-terminated strings to avoid unnecessary recomputation of string lengths, which can lead to more efficient programming practices.
- The `strlcpy` function's performance varies significantly between OpenBSD and glibc implementations.
- Glibc's use of optimized `strlen` and `memcpy` results in faster execution despite traversing the string twice.
- Instruction-level parallelism (ILP) and dependencies in code can greatly impact performance.
- The article suggests moving away from null-terminated strings to sized strings for better efficiency.
- Understanding CPU behavior is essential for effective performance optimization in programming.
Related
Designing a Better Strcpy
Saagar Jha explores challenges in enhancing strcpy in C, proposing strxcpy for efficient, null-terminated string copying with overflow indication. Comparison of strcpy variants reveals strscpy's functionality superiority but standardization absence. Jha notes original bug and C string handling complexities, emphasizing efficiency, safety, and standardization in strcpy evolution.
I'm Not a Fan of Strlcpy(3)
strlcpy is debated for efficiency compared to strcpy and strncpy. For optimal performance, memccpy is suggested over strlcpy or strncpy. Dynamic allocation or mem* functions are preferred for string operations.
Clang vs. Clang
The blog post critiques compiler optimizations in Clang, arguing they often introduce bugs and security vulnerabilities, diminish performance gains, and create timing channels, urging a reevaluation of current practices.
Parsing protobuf at 2+GB/s: how I learned to love tail calls in C (2021)
The Clang compiler's `musttail` attribute ensures tail call optimization, enhancing performance in C-based interpreters and parsers, particularly improving Protocol Buffers parsing speed to over 2GB/s.
Do low-level optimizations matter? Faster quicksort with cmov (2020)
The article emphasizes the importance of low-level optimizations in sorting algorithms, highlighting how modern CPU features and minimizing conditional branches can enhance performance, particularly with the new `swap_if` primitive.
0 commentsRelated
Designing a Better Strcpy
Saagar Jha explores challenges in enhancing strcpy in C, proposing strxcpy for efficient, null-terminated string copying with overflow indication. Comparison of strcpy variants reveals strscpy's functionality superiority but standardization absence. Jha notes original bug and C string handling complexities, emphasizing efficiency, safety, and standardization in strcpy evolution.
I'm Not a Fan of Strlcpy(3)
strlcpy is debated for efficiency compared to strcpy and strncpy. For optimal performance, memccpy is suggested over strlcpy or strncpy. Dynamic allocation or mem* functions are preferred for string operations.
Clang vs. Clang
The blog post critiques compiler optimizations in Clang, arguing they often introduce bugs and security vulnerabilities, diminish performance gains, and create timing channels, urging a reevaluation of current practices.
Parsing protobuf at 2+GB/s: how I learned to love tail calls in C (2021)
The Clang compiler's `musttail` attribute ensures tail call optimization, enhancing performance in C-based interpreters and parsers, particularly improving Protocol Buffers parsing speed to over 2GB/s.
Do low-level optimizations matter? Faster quicksort with cmov (2020)
The article emphasizes the importance of low-level optimizations in sorting algorithms, highlighting how modern CPU features and minimizing conditional branches can enhance performance, particularly with the new `swap_if` primitive.