setup

Host setup

Bring a fresh machine to a state where PACT can run. Do this before building ../src/ or using ../run/.

Subdir	Purpose
kernel/	Build, install, and boot vanilla Linux 6.3, then build and load the two modules the tiering subsystem requires - tierinit (registers the slow tier + demotion targets) and kswapdrst (keeps kswapd/demotion from stalling).
env/	Prepare the machine for controlled runs: uncore-frequency pinning, CXL/NUMA layout, performance governor, and disabling turbo / THP / KSM / NUMA-balancing.
perf/	Build the PAC-patched perf used for PAC sampling (install-perf.sh clones Linux v5.15, applies pac_perf.patch, and builds the perf binary).

Order

1. Kernel - kernel/: setup_kernel.sh → reboot into 6.3 → build_modules.sh.
2. Environment - env/: sudo ./prepare_environment.sh (or let the runner do it via run_setup_config=true ./run-pact.sh ...).

The env scripts source each other by their own location, so they can be invoked from anywhere (e.g. the runner calls ../setup/env/prepare_environment.sh).

Validate the CXL emulation (important)

The slow tier is emulated by a remote NUMA node with its CPUs taken offline and its uncore frequency pinned low. check_cxl_conf now aborts if Node 1 still has online CPUs (an unvalidated layout silently produces invalid results). Two things are not auto-validated and you should confirm them:

1. Topology - after prepare_environment.sh, the slow-tier node must be CPU-less:

   numactl --hardware        # 'node 1 cpus:' should be empty

2. Latency - the emulated tiers should land near the paper's targets (~90 ns local DRAM, ~140 ns remote NUMA, ~190 ns CXL-emulated; see ../modeling/README.md). Measure with a pointer-chase latency tool (e.g. Intel MLC --latency_matrix, or the ptr_chase microbenchmark) and adjust the uncore-frequency targets in env/modify-uncore-freq.sh / UNCORE_ARGS until the slow tier matches. Pinning the frequency without checking the resulting latency is the most common source of invalid tiering results.

Set the local (fast-tier) DRAM size

Use memmap on the GRUB cmdline to reserve DRAM and shrink the fast tier.

Example: CloudLab c220g5 has 96 GB DRAM per socket. Adding memmap=76G!2G to GRUB_CMDLINE_LINUX reserves 76 GB starting at 2 GB. After update-grub and reboot: node 0 size: 20730 MB; node 0 free: 18746 MB. The values vary by ~hundreds of MB each boot - tune carefully.

Notes

• The current scripts assume a 2-NUMA-node server (one fast tier, one CXL-like slow tier).