3 ms·

I’m working on a masters thesis doing essentially this, for the problem of prefetching. There are a lot of existing papers demonstrating techniques for smarter

I’m working on a masters thesis doing essentially this, for the problem of prefetching. There are a lot of existing papers demonstrating techniques for smarter prefetching for non- sequential data structures like trees and graphs. That can be done with some success purely at the hardware level, but having language- level semantic information helps a lot for dealing with complex data structures. What I’m working on is a cache controller modification to allow the running program or OS to tell the cache controller how best to prefetch specific pieces of data.

jacknews 3y ago
"having language- level semantic information helps a lot for dealing with complex data structures." Yes that's what I'm thinking - much of the current stuff seems to be trying to guess what the code is doing from a low level (eg branch prediction) whereas the language itself could tell.
mhh__ 3y ago
I'm pretty sure I've read a PhD thesis that implements exactly that - e.g. the program can load a program into the prefetcher Sounds like a nightmare post-spectre.
- jakeinspace 3y ago
  Definitely possible, it’s a fairly active area. There are a few very similar techniques I’ve seen covered, but I think the details of my/our approach are still unique enough to merit publishing (for now), if I can get reasonable performance results. And yes, loading semi-arbitrary code into a prefetcher is quite scary. It was the first question I had about this project. I think that maybe picking and choosing one of a multitude of prefetching "recipes" which are trusted would be more plausible as en eventual viable strategy. Like, the compiler inserts some instructions after allocating the nodes of a DAG that says "hey prefetcher, this is a DAG, please choose the graph prefetching algo with x/y/z parameters."

3 ms·

I’m working on a masters thesis doing essentially this, for the problem of prefetching. There are a lot of existing papers demonstrating techniques for smarter

by jakeinspace 3y ago

jacknews 3y ago
"having language- level semantic information helps a lot for dealing with complex data structures." Yes that's what I'm thinking - much of the current stuff seems to be trying to guess what the code is doing from a low level (eg branch prediction) whereas the language itself could tell.
mhh__ 3y ago
I'm pretty sure I've read a PhD thesis that implements exactly that - e.g. the program can load a program into the prefetcher Sounds like a nightmare post-spectre.
- jakeinspace 3y ago
  Definitely possible, it’s a fairly active area. There are a few very similar techniques I’ve seen covered, but I think the details of my/our approach are still unique enough to merit publishing (for now), if I can get reasonable performance results. And yes, loading semi-arbitrary code into a prefetcher is quite scary. It was the first question I had about this project. I think that maybe picking and choosing one of a multitude of prefetching "recipes" which are trusted would be more plausible as en eventual viable strategy. Like, the compiler inserts some instructions after allocating the nodes of a DAG that says "hey prefetcher, this is a DAG, please choose the graph prefetching algo with x/y/z parameters."