# Interaction to Next Paint Changes in Chrome 122
## Enable EventTimingMatchPresentationIndex by default
Events measured by Event Timing typically measure to Next Paint (and its
presentation time). But sometimes we don't need a next paint, and can end
measurement immediately at processingEnd.
This detail come sometimes lead to multiple distinct events overlapping in time
in non-intuitive ways. As one example:
Let's say and event (A) arrives first, and requires next paint. It will
measure:
* Input delay (for Event A)
* Processing Duration (for Event A)
* Presentation delay (for this Animation Frame)
Because waiting for Presentation delay is not blocking the main thread, another
event (B) might arrive next. If Event B does not require next paint, it will
only measure:
Input delay (for Event B)
Processing Duration (for Event B)
Now, even thought Event B arrived after Event A, its performance Event Timing
measurement might be completed first... whenever we're still waiting to receive
Event A's presentation time.
In such cases, even though performance measurement for Event B "wraps up"
first, we cannot assume that Event B actually ends first. This is because it
takes time to schedule the feedback of a presentation time, which is itself an
asynchronous process. And even when the measurement accounting work for Event B
is available first, once we read the presentation time value for Event A, it
might have actually been first.
Previously, whenever this happened, we would flush all event timings and assign
the current time as the end time to all these events, even those waiting for
the next paint presentation time. Now, we will wait until the correct next
paint presentation time actually arrives for those events.
Note: this experiment was first landed in Chrome 114: [Event Timing Presentation Promise Handling Redesign](https://chromium.googlesource.com/chromium/src/+/ce150839f2930a7d59b3850ca8e7d02210101f08),
but was rolled out slowly.
## How does this affect a site's metrics?
This change improves the quality/accuracy of INP, but its impact on a specific
site is unpredictable and can be different case by case depending on use cases.
In general, we saw a overall decrease on INP on mobile and an increase on INP
on desktop.
## When were users affected?
Chrome 122 was released the week of February 20, 2024.
Codebase Browser
chromium