The scroll path copied every pixel row up by one glyph height, READING
video memory — and VRAM reads are uncached-slow on real hardware.
Measured on the 16-core PC: ~90 seconds to bring the cores online,
almost entirely boot-transcript lines each paying a whole-screen scroll
copy. (QEMU never shows this: its 'VRAM' is host RAM.)
When the screen fills, the console now clears and restarts at the top —
writes only, once per screenful. The transcript reads the same as it
streams; only the scrollback illusion is gone, which a boot console
never needed.
Daniel Samson
f587e7e05e