Terminal and shell performance

Re:Terminal and shell performance by JohnBooty on Tuesday July 18, 2017 @09:08PM (#14801363)

   You only need to be as fast as one screen refresh 
   period, 1/60th of a second usually, plenty of 
   cycles on modern cpus. Many games that are very 
   complex graphically do it without problem

Sorry, no. You're totally conflating two orthogonal concepts: throughput and latency.

Rendering 60fps (or even 1,000fps) is not remotely the same as achieving low latency.

Even if a game is rendering at 60fps, input latency (the time between a user clicking a button and something happening on the screen) is often over 100ms.

This article breaks it down... there's a link to it in the original story about terminal latency posted by OP:

http://renderingpipeline.com/2013/09/measuring-input-latency...

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Re:Terminal and shell performance by MaulingMonkey on Tuesday July 18, 2017 @11:33PM (#14801863)

Some of the listed problems are throughput problems, not latency problems (both in this thread and the original article), so it's not a mistake to address both types of performance problems. And while throughput and latency might be orthogonal concepts, they're not nearly so orthogonal in practice when optimizing. Reducing e.g. an average 48ms frame time, or a 100+ms frame stall, will improve both throughput and worst case latency. There are a few optimizations which focus more exclusively on one or the other, but my experience is that they tend to be rarer.

Your reply also reads like games are getting away with introducing 100s of milliseconds of additional latency, which just isn't the case for the most part. There is hardware and kernel buffering that userland software can do little about, admittedly, that can easily add up to getting you above 100ms as you say. Even there, some improvements can be made:

Gsync reduces latency by getting rendered frames displayed as quickly as possible, by tying refresh rates to frame rates. "Time warp" reprojects rendered scenes shortly before refresh to help reduce latency between head movements and screen movements in VR - but this is also effectively "improving" throughput and worst case latency, by ensuring there's always a new head-rotated frame - even if the main scene renderer wasn't able to provide a full scene update yet. There's some talk of going back to single buffering and chasing the beam, although I'm skeptical if that'll actually happen for anything but the most niche applications.

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