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Chaitanya Kumar's Blog

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Counting Counters on Zen 4: Identifying the Cause of a Segfault using my CPU's Manual

Introduction While working on my previous blog post , I had tried to use likwid-perfctr instead of perf-stat . likwid-perfctr -e segfaulted on my machine. This article goes into how I triaged this issue and reported it to the LIKWID devs. It was “fun” in the way that having to open your CPU’s processor programming reference manual is fun. The Crash Just like perf stat ,…

Accelerating copy_if using SIMD

Introduction I have a Zen 4 CPU with a bunch of AVX512 feature flags. So I thought - let’s try and use it to implement something, even if it’s in the realm of wheel-reinvention. I started with the following goals. Implement an algorithm that cannot be vectorized by my optimizing compiler, even with a polyhedral loop model. Systematically analyze its performance and answer the questions…