// CPU A ready_flag = 1; data = 42; // Intended to be written BEFORE the flag // CPU B if (ready_flag) print(data); // On Alpha: prints 0, not 42
Today, as we run workloads on 192-core ARM servers and GPUs with 18,000 threads, we are still fighting the same war. The architectures are more "modern," but the PDF from 1994 remains the Rosetta Stone. unix systems for modern architectures -1994- pdf
A process migrated from CPU 0 to CPU 1 would find its L1 cache cold. It would run 3x slower for the first 10ms. // CPU A ready_flag = 1; data =
To a casual user, it looks like a dry technical specification. But to a systems programmer or a digital archaeologist, those five words tell a dramatic story. 1994 was the year Unix faced its existential crisis. The "modern architectures" of the time—the MIPS R4000, the DEC Alpha, the HP PA-RISC, and the nascent Intel Pentium—were tearing apart the old assumptions of the 1970s and 80s. It would run 3x slower for the first 10ms