On Thu, 22 Feb 2018 23:35:45 +1100 Michael Ellerman mpe@ellerman.id.au wrote:
From: Nicholas Piggin npiggin@gmail.com
commit bdcb1aefc5b3f7d0f1dc8b02673602bca2ff7a4b upstream.
The fallback RFI flush is used when firmware does not provide a way to flush the cache. It's a "displacement flush" that evicts useful data by displacing it with an uninteresting buffer.
The flush has to take care to work with implementation specific cache replacment policies, so the recipe has been in flux. The initial slow but conservative approach is to touch all lines of a congruence class, with dependencies between each load. It has since been determined that a linear pattern of loads without dependencies is sufficient, and is significantly faster.
Measuring the speed of a null syscall with RFI fallback flush enabled gives the relative improvement:
P8 - 1.83x P9 - 1.75x
The flush also becomes simpler and more adaptable to different cache geometries.
Signed-off-by: Nicholas Piggin npiggin@gmail.com [mpe: Backport to 4.9] Signed-off-by: Michael Ellerman mpe@ellerman.id.au
Thanks for doing these. They all look okay to me.
Thanks, Nick