Timestamps need to be in nanoseconds

[Wumpf]

Timestamp values are supposed to represent nanosecond values, see https://gpuweb.github.io/gpuweb/#timestamp
Meaning that get_timestamp_period has to go.
Instead, wgpu-core needs to add a compute shader that converts timestamps with a previously acquired tick->ns ratio upon query resolve. See also gpuweb/gpuweb#1325 (comment)

Related to

• Implement Timestamp Queries on Metal #2739
• feature: Timestamp queries #3636
• Write timestamp lands on wrong side of barriers #2521

[cwfitzgerald]

I'm honestly not convinced that this is something we should require this on native. We need the functionality in wgpu-core so moz can implement it for WebGPU, but on native, "compute shader injection" isn't going to sit terribly well with our users.

[cwfitzgerald]

To note - this get_timestamp_period was specifically designed to work fine with the WebGPU model as well while giving us a overhead free version on native (webgpu always reports 1).

Honestly I don't get why the committee settled on this rather silly (imo) design.

[Wumpf]

Oh I see, though this is just an artifact of how things developed over time.
I'm also not happy with the commitee decision on this one, but it also doesn't sit right with me that only for native one needs to use the value - this means that wgpu interface has a more relaxed spec than the WebGPU spec. Sure it has a lot of "extras" via native features, but this feels different to me as it actually changes the meaning of a value from the interface depending on whether you run on web native. Essentially putting a lil dent into portability.

Isn't this also an issue for correctly implementing the webgpu native header correctly?
Mozilla may implement this as a layer over query resolve, but it's not great either.

Not a hill I'll die on as I wouldn't want to volunteer for that compute shader either 😄

[cwfitzgerald]

No matter what, wgpu-core needs to implement this in resolve, if only for the needs of firefox and maybe wgpu-native.

I'm basically of the mind where if there is an api we can design that allows our native users to not have to suffer the consequences of interesting WebGPU decisions, I'd much rather see that then us just fully copy WebGPU.

[Diggsey]

My terminology might be a bit out of date, but when creating a device users could request what timestamp period to use, with two options, "Native" or "Nanosecond". If the user requests "Nanosecond" then "get_timestamp_period" would be guaranteed to return 1.

[Wumpf]

thought about this again and agreeing with @cwfitzgerald . Updating comment on get_timestamp_period in #3636 a little bit