[Libre-soc-isa] [Bug 598] New: Approaching Zero Latency

bugzilla-daemon at libre-soc.org bugzilla-daemon at libre-soc.org
Mon Feb 15 03:58:36 GMT 2021


            Bug ID: 598
           Summary: Approaching Zero Latency
           Product: Libre-SOC's first SoC
           Version: unspecified
          Hardware: Other
                OS: Linux
            Status: CONFIRMED
          Severity: enhancement
          Priority: ---
         Component: Specification
          Assignee: programmerjake at gmail.com
          Reporter: programmerjake at gmail.com
                CC: libre-soc-isa at lists.libre-soc.org,
                    programmerjake at gmail.com
   NLnet milestone: ---

I had an interesting idea: You know how GPU manufacturers have been increasing
display fps like crazy? (Some monitors are up to 360fps iirc) The real reason
is it reduces overall system latency -- from mouse/keyboard/etc. to pixels
lighting up on the screen. So, why don't we try to design it so we can reduce
latency to 10s/100s of microseconds by instead designing the system in a
streaming fashion, so we render a few scan-lines before we send it to the
display, rather than having to render a full screen before we start sending it
to the display. Also, we take adaptive sync (variable refresh rate) to its
logical extreme and can delay on the level of small groups of pixels if
rendering is taking too long (can be done in DisplayPort since it's packet
based, but obviously it breaks the current spec, I'd expect at least some
displays to support this, unintentionally of course).

We can also have mechanisms to allow the scan-out engine to translate (move)
the displayed picture partway through scanning-out a frame (potentially with
sub-pixel resolution, interpolating the colors), interpolating the translation
amount in time to smooth out the tearing you'd otherwise get.
Adding this to Vulkan shouldn't be that difficult, for full-screen games at
least. In particular, this would be very useful for VR, since low latency is a
necessity to avoid nausea.

This would allow us to achieve a lot of the benefits of extremely high refresh
rates at a lower refresh rate, with power savings to match.

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