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Andrea Righi fc889c6995 scx_rustland: replace custom allocator with buddy-alloc 
Currently, the primary bottleneck in scx_rustland lies within its custom
memory allocator, which is used to prevent page faults in the user-space
scheduler.

This is pretty evident looking at perf top:

  39.95%  scx_rustland             [.] <scx_rustland::bpf::alloc::RustLandAllocator as core::alloc::global::GlobalAlloc>::alloc
   3.41%  [kernel]                 [k] _copy_from_user
   3.20%  [kernel]                 [k] __kmem_cache_alloc_node
   2.59%  [kernel]                 [k] __sys_bpf
   2.30%  [kernel]                 [k] __kmem_cache_free
   1.48%  libc.so.6                [.] syscall
   1.45%  [kernel]                 [k] __virt_addr_valid
   1.42%  scx_rustland             [.] <scx_rustland::bpf::alloc::RustLandAllocator as core::alloc::global::GlobalAlloc>::dealloc
   1.31%  [kernel]                 [k] _copy_to_user
   1.23%  [kernel]                 [k] entry_SYSRETQ_unsafe_stack

However, there's no need to reinvent the wheel here, rather than relying
on an overly simplistic and inefficient allocator, we can rely on
buddy-alloc [1], which is also capable of operating on a preallocated
memory buffer.

After switching to buddy-alloc, the performance profile under the same
workload conditions looks like the following:

   6.01%  [kernel]                 [k] _copy_from_user
   5.21%  [kernel]                 [k] __kmem_cache_alloc_node
   4.45%  [kernel]                 [k] __sys_bpf
   3.80%  [kernel]                 [k] __kmem_cache_free
   2.79%  libc.so.6                [.] syscall
   2.34%  [kernel]                 [k] __virt_addr_valid
   2.26%  [kernel]                 [k] _copy_to_user
   2.14%  [kernel]                 [k] __check_heap_object
   2.10%  [kernel]                 [k] __check_object_size.part.0
   2.02%  [kernel]                 [k] entry_SYSRETQ_unsafe_stack

With this change in place, the primary overhead is now moved to the
bpf() syscall and the copies between kernel and user-space (this could
potentially be optimized in the future using BPF ring buffers, instead
of BPF FIFO queues).

A better focus at the allocator overhead before vs after this change:

 [before]
 39.95%  scx_rustland  [.] core::alloc::global::GlobalAlloc>::alloc
  1.42%  scx_rustland  [.] core::alloc::global::GlobalAlloc>::dealloc

 [after]
  1.50%  scx_rustland  [.] core::alloc::global::GlobalAlloc>::alloc
  0.76%  scx_rustland  [.] core::alloc::global::GlobalAlloc>::dealloc

[1] https://crates.io/crates/buddy-alloc

Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
2024-02-11 14:33:39 +01:00
..
scx_layered scx_layered: Use scx_utils::user_exit_info 2024-01-31 10:54:20 -10:00
scx_rustland scx_rustland: replace custom allocator with buddy-alloc 2024-02-11 14:33:39 +01:00
scx_rusty scx: Implement solution to infeasible weights problem 2024-02-09 16:23:12 -06:00
meson.build scx_rustland: rename from scx_rustlite 2023-12-22 00:20:14 +01:00
README.md Add README files for each rust scheduler 2024-01-04 07:35:44 -08:00

README.md

RUST SCHEDULERS

Introduction

This directory contains schedulers with user space rust components.

The README in each scheduler directory provides some background and describes the types of workloads or scenarios they're designed to accommodate. For more details on any of these schedulers, please see the header comment in their main.rs or *.bpf.c files.

Schedulers