llcctl

A numactl-like launcher for per-process cache aware scheduling control, built on prctl(PR_SCHED_CACHE) (the cache_aware_dev_prctl kernel series).

llcctl sets the requested attributes on itself, marks them as inheritable across execve(), and executes the command. Because fork() children always inherit the attributes and the inherit mask survives both fork() and execve(), the whole process tree of the command runs with the given settings. Nested invocations compose (the inherit bits are OR-ed).

Build

make            # needs any libc; kernel headers optional
                # (uapi constants have a built-in fallback)

Usage

llcctl [options] [--] command [args...]
llcctl --show

option	attribute	meaning
-e / -d	PR_SCHED_CACHE_ENABLE	opt in / out while the feature is globally on
-n, --tolerance-nr=N	AGGR_TOLERANCE_NR	allow ~N running threads per physical core of one LLC (0..100, default)
-s, --tolerance-size=N	AGGR_TOLERANCE_SIZE	memory footprint tolerance (0..100, default)
-p, --overaggr-pct=N	OVERAGGR_PCT	LLC busy threshold, percent of LLC capacity (0..1000, default)
-S, --show		print the calling process's attributes

default (or -1) resets an attribute to follow the global debugfs knobs under /sys/kernel/debug/sched/llc_balancing/.

Examples

# opt a memory-bandwidth-hungry workload out of aggregation, so
# its threads spread across LLCs and use their combined bandwidth
llcctl -d -- ./membw-hungry

# pack a Verilator-style job: up to ~2 threads per physical core
# in one LLC, LLC considered non-busy up to 100% of capacity
llcctl -n 2 -p 100 -- make -j16

# inspect what a shell inherited
llcctl --show

Notes

• The effective thread cutoff is roughly 0.8 * N * cores + 3 per LLC (the 0.8 is fits_capacity() headroom, the +3 the EWMA rounding), e.g. on an 8c/16t LLC: -n 1 ≈ 9 threads, -n 2 ≈ 15.
• Attributes only take effect while the feature is globally enabled (llc_balancing/enabled = 1) on hardware with multiple LLCs; llcctl cannot turn the feature on by itself.
• Exit codes follow env(1): 125 llcctl error, 126 command not executable, 127 command not found.

License

GPL-2.0-only, the same license as the Linux kernel — see COPYING.