LGTM2
100 microseconds sound very coarse for this, but I guess that just means
they have to average data over many frames. And if they are happy, I'm
happy.
/Daniel
On 2023-11-08 09:41, Yoav Weiss wrote:
LGTM1
Thanks for working through this issue!!
On Wed, Nov 8, 2023 at 2:34 AM Domenic Denicola <[email protected]>
wrote:
On Tue, Nov 7, 2023 at 5:42 PM François Beaufort
<[email protected]> wrote:
On Mon, Oct 30, 2023 at 7:39 PM Mike Taylor
<[email protected]> wrote:
On 10/30/23 12:59 PM, Corentin Wallez wrote:
On Fri, Oct 27, 2023 at 2:19 AM Domenic Denicola
<[email protected]> wrote:
On Thu, Oct 26, 2023 at 7:21 PM François Beaufort
<[email protected]> wrote:
On Thu, Oct 26, 2023 at 11:05 AM Domenic Denicola
<[email protected]> wrote:
On Thu, Oct 26, 2023 at 5:21 PM 'François
Beaufort' via blink-dev
<[email protected]> wrote:
Contact emails
[email protected], [email protected]
Explainer
https://github.com/gpuweb/gpuweb/issues/614
<https://github.com/gpuweb/gpuweb/issues/614>
Specification
https://gpuweb.github.io/gpuweb/#timestamp
<https://gpuweb.github.io/gpuweb/#timestamp>
Summary
WebGPU timestamp queries allow WebGPU
applications to measure precisely (down
to the nanosecond) how much time their
GPU commands take to execute, especially
at the beginning and end of passes.
Timestamp queries are heavily used to
gain insights into the performance and
behavior of GPU workloads.
While the WebGPU specification makes
timestamp queries an optional feature due
to timing attack concerns, we believe
that timestamp queries quantization
provides a good middle ground by reducing
the precision of timers. To offer even
more advanced protection against timing
attacks and fingerprinting, timestamp
queries are also coarsened based on site
isolation status:
- Isolated contexts: timestamp queries
are exposed with a resolution of 100
microseconds.
- Non-isolated contexts: timestamp
queries are not exposed at all.
By "isolated" do you mean "has the
cross-origin isolated capability
<https://html.spec.whatwg.org/#concept-settings-object-cross-origin-isolated-capability>"?
Yes.
I wasn't able to find any spec or tests for
this requirement, which seems like a
potential interoperability issue.
The WebGPU spec currently says: "The feature is
optional, and a WebGPU implementation may limit
its exposure only to those scenarios that are
trusted."
See
https://gpuweb.github.io/gpuweb/#security-timing:~:text=The%20feature%20is%20optional%2C%20and%20a%20WebGPU%20implementation%20may%20limit%20its%20exposure%20only%20to%20those%20scenarios%20that%20are%20trusted
I realize that. I was suggesting that, for
interoperability purposes, you should consider
specifying the actual condition, instead of leaving
it vague and optional. (E.g. at least in other
standards bodies, we have guidance to avoid optional
or implementation-defined features; instead, we try
to work together with other browser engines to come
to a common, interoperable implementation, backed by
a test suite.)
I hope the API Owners can consider this when deciding
whether or not to approve, as I believe that letting
these sorts of non-specified and non-tested features
be shipped is harmful for the platform's health.
I'll add discussion of that to the agenda for this week's
WebGPU meeting: can we agree on the availability of
timestamp queries (provided there is hardware support)
and the quantization depending on contexts. (but to be
perfectly honest I think we'll have pushback). Of course
the WebGPU standard body tries to avoid
implementation-defined features, and instead have
deterministic and tested features, but timestamps is one
of the ones that might need to be an exception to it.
Let's see what consensus the group comes to!
Thank you - looking forward to the update.
Good news! The members of the GPU for the Web Community Group
have accepted a proposal
<https://github.com/gpuweb/gpuweb/issues/4175#issuecomment-1789865938>
to allow timestamps regardless of site isolation, always with
the non-isolated resolution from hr-time
<https://w3c.github.io/hr-time/#dfn-coarsen-time> (100us).
Check out the spec PR at
https://github.com/gpuweb/gpuweb/pull/4359 and updated spec at
https://gpuweb.github.io/gpuweb/#security-timing. This
decision aims to address the interoperability concerns raised
earlier.
That's great! Using the same time resolution as the rest of the
platform makes sense, and this definitely addresses my interop
concerns. Thanks to you and the group for making this change!
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