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A comment on LatencyFleX: A new approach to game latency reduction. Parent comment

Re:LatencyFleX: A new approach to game latency reduction by snarfy on Monday January 10, 2022 @10:51AM (#29876648)
There are a variety of factors that add up to many ms of lag. USB and HDMI are a few that come to mind. USB is incredibly complex when compared to e.g. ps/2. If you are building an embedded board like rasberry pi and you want to add ps/2, you just add a couple pins. If you want to add usb, you buy an extra chip.
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Re:LatencyFleX: A new approach to game latency reduction by duped on Monday January 10, 2022 @11:30AM (#29877282)
Many CPUs have USB support. Pin count also doesn't correlate to latency, what matters is the minimum buffer size and transfer speed.

USB can beat PS/2 for latency without issue.

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Re:LatencyFleX: A new approach to game latency reduction by WithinReason on Monday January 10, 2022 @12:20PM (#29878099)
Isn't PS/2 interrupt based, while USB is based on periodic polling?
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Re:LatencyFleX: A new approach to game latency reduction by duped on Monday January 10, 2022 @01:41PM (#29879425)
Polling is often lower latency than interrupts on modern hardware, since it can run at much finer grains and has so much less overhead to startup over an ISR.
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Re:LatencyFleX: A new approach to game latency reduction by wtallis on Monday January 10, 2022 @01:47PM (#29879560)
That's often true on a scale of microseconds, but USB input devices are polled at intervals on millisecond scale.
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Re:LatencyFleX: A new approach to game latency reduction by cma on Monday January 10, 2022 @02:03PM (#29879893)
Only in the slowest modes. It is possible to go faster than the 1ms poll rate, though it is back to interrupts:

> Transaction latency

> For low speed (1.5 Mbit/s) and full speed (12 Mbit/s) devices the shortest time for a transaction in one direction is 1 ms.[6] High speed (480 Mbit/s) uses transactions within each micro frame (125 µs)[7] where using 1-byte interrupt packet results in a minimal response time of 940 ns. 4-byte interrupt packet results in 984 ns.

https://www.wikipedia.org/wiki/USB_(Communications)

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Re:LatencyFleX: A new approach to game latency reduction by bschwindHN on Monday January 10, 2022 @07:23PM (#29885248)
Ben Eater has a good video on this:

https://youtu.be/wdgULBpRoXk?t=1765

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Re:LatencyFleX: A new approach to game latency reduction by hffftz on Monday January 10, 2022 @10:59AM (#29876786)
> If you want to add usb, you buy an extra chip.

Do you know how many chips are in a cable modem/router combo?

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Re:LatencyFleX: A new approach to game latency reduction by formerly_proven on Monday January 10, 2022 @11:02AM (#29876823)
1 or 2, depends on the kind of modem. VDSL2+ modems might have three, though one of those is the line driver which is zero-delay for the purposes of a computer.
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Re:LatencyFleX: A new approach to game latency reduction by hffftz on Monday January 10, 2022 @11:14AM (#29877015)
I've seen many more chips last time I opened one....
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Re:LatencyFleX: A new approach to game latency reduction by jaywalk on Monday January 10, 2022 @12:32PM (#29878323)
Most of those chips have zero impact on latency, and many aren't even involved in the actual packet flow.
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Re:LatencyFleX: A new approach to game latency reduction by ben-schaaf on Monday January 10, 2022 @11:33AM (#29877346)
Modems/routers don't use polling nor do they need debouncing. The default USB polling rate is 125Hz, which is already 8ms of latency. Debouncing depends on the switch and is generally a couple milliseconds as well.
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