Daniel Lemire is a software performance expert. He ranks among the top 2% of scientists globally (Stanford/Elsevier 2025) and is one of GitHub's top 1000 most followed developers.
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People still tell me that CPUs are boring. That nothing much happens anymore. Let us look at AMD Ryzen 7 processors from 2022 to 2024: the 5800X3D (Zen 3), the 7800X3D (Zen 4) and the 9800X3D (Zen 5). They are comparable 8-core chips with 3D V-Cache. I have written about them before, in How stagnant … Continue reading…
Some of the latest Intel processors support the AVX-512 family of vector instructions. These instructions operate on blocks of 512 bits (or 64 bytes). The benefit of such wide instructions is that even without increasing the processor clock speed, systems can still process a lot more data. Most code today operators…
When a program is mostly just accessing memory randomly, a standard cost model is to count the number of distinct random accesses. The general idea is that memory access is much slower than most other computational tasks. Furthermore, the cost model can be extended to count "nearby" memory accesses as free. That is…
In my previous blog post, I compared the performance of my new ARM-based MacBook Pro with my 2017 Intel-based MacBook Pro. I used a number parsing benchmark. In some cases, the ARM-based MacBook Pro was nearly twice as fast as the older Intel-based MacBook Pro. I think that the Apple M1 processor is a breakthrough ……
If I multiply two 64-bit integers (having values in [0, 264)), the product requires 128 bits. Intel and AMD processors (x64) can compute the full (128-bit) product of two 64-bit integers using a single instruction (mul). ARM processors, such as those found in your mobile phone, require two instructions to achieve the…
When benchmarking software, we often start by measuring the time elapsed. If you are benchmarking data bandwidth or latency, it is the right measure. However, if you are benchmarking computational tasks where you avoid disk and network accesses and where you only access a few pages of memory, then the time elapsed is…
Note: This blog post from 2018 predates the Intel Ice Lake (Sunny Core) and AMD Zen 4 processors. These newer processors are not affected by the issues described in this blog post. Our processors typically do computations using small data stores called registers. On 64-bit processors, 64-bit registers are frequently…
In about 10 years, Apple has multiplied by 19 the number of transistors in its mobile processors. It corresponds roughly to a steady rate of improvement of 34% per year on the number of transistors, or a doubling every 2.5 years. In real dollars, an iPhone has roughly a constant price: the price tag of … Continue…
Modern processors execute instructions in parallel in many different ways: multi-core parallelism is just one of them. In particular, processor cores can have several outstanding memory access requests "in flight". This is often described as "memory-level parallelism". You can measure the level of memory-level…
Modern processors have the ability to execute many instructions per cycle, on a single core. To be able to execute many instructions per cycle in practice, processors predict branches. I have made the point over the years that modern CPUs have an incredible ability to predict branches. It makes benchmarking difficult…
In my previous post, I reviewed a new fast random number generator called wyhash. I commented that I expected it to do well on x64 processors (Intel and AMD), but not so well on ARM processors. Let us review again wyhash: uint64_t wyhash64_x; uint64_t wyhash64() { wyhash64_x += 0x60bee2bee120fc15; __uint128_t tmp; tmp…
The performance of a processor is determined by several factors. For example, processors with a higher frequency tend to do more work per unit of time. Physics makes it difficult to produce processors that have higher frequency. Modern processors can execute many instructions per cycle. Thus a 3.4GHz processor has 3.4…
Up to yesterday, my laptop was a large 15-inch MacBook Pro. It contains an Intel Kaby Lake processor (3.8 GHz). I just got a brand-new 13-inch 2020 MacBook Pro with Apple's M1 ARM chip (3.2 GHz). How do they compare? I like precise data points. Recently, I have been busy benchmarking number parsing routines where you…
Suppose that I give you a relatively long string and you want to remove all spaces from it. In ASCII, we can define spaces as the space character (' '), and the line ending characters ('\r' and '\n'). I am mostly interested in algorithmic and performance issues, so we can simplify the problem by removing all ……