“Terminal Latency”, Dan Luu2017-07-18 (computer hardware, Emacs, DNB; backlinks)⁠:

These graphs show the distribution of latencies for each terminal. The y-axis has the latency in milliseconds. The x-axis is the percentile (eg. 50 means represents 50%-ile keypress ie. the median keypress). Measurements are with macOS unless otherwise stated. The graph on the left is when the machine is idle, and the graph on the right is under load. If we just look at median latencies, some setups don’t look too bad—terminal.app and emacs-eshell are at roughly 5ms unloaded, small enough that many people wouldn’t notice. But most terminals (st, alacritty, hyper, and iterm2) are in the range where you might expect people to notice the additional latency even when the machine is idle. If we look at the tail when the machine is idle, say the 99.9%-ile latency, every terminal gets into the range where the additional latency ought to be perceptible, according to studies on user interaction. For reference, the internally generated keypress to GPU memory trip for some terminals is slower than the time it takes to send a packet from Boston to Seattle and back, about 70ms.

…Most terminals have enough latency that the user experience could be improved if the terminals concentrated more on latency and less on other features or other aspects of performance. However, when I search for terminal benchmarks, I find that terminal authors, if they benchmark anything, benchmark the speed of sinking stdout or memory usage at startup. This is unfortunate because most “low performance” terminals can already sink stdout many orders of magnitude faster than humans can keep up with, so further optimizing stdout throughput has a relatively small impact on actual user experience for most users. Likewise for reducing memory usage when an idle terminal uses 0.01% of the memory on my old and now quite low-end laptop. If you work on a terminal, perhaps consider relatively more latency and interactivity (eg. responsiveness to ^C) optimization and relatively less throughput and idle memory usage optimization.

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