megboyzzandClaude
daa537bfe8
Two results, one positive and one negative.
CONFIRMED - removing the exit-request check from the guest load/store path
(ea079b8) is worth 6.3%. That commit went in on a single A/B pair because
the device wedged mid-measurement; re-run on a freshly rebooted Pixel 6a,
three interleaved pairs, load to first OnCarLoaded:
without the check: 33.42 / 33.10 / 33.32 s mean 33.28
with the check: 35.62 / 35.43 / 35.49 s mean 35.51
Ranges do not overlap and each spread is under a third of a second.
REFUTED - raising CPU_TLB_DYN_DEFAULT_BITS from 8 to 12. The premise checked
out: a probe in tlb_mmu_resize_locked showed it runs only about twice per
second and current_entries stayed at 256 for a whole run, so the adaptive
TLB genuinely never grows for this workload and sits at 1 MB of coverage
against a working set of hundreds of MB.
Raising it took effect (current_entries=4096, verified live) and bought
nothing:
12 bits: 32.36 / 32.26 s
8 bits: 32.86 / 32.32 s 0.28s apart, ranges overlap
The profile moved the WRONG way - tlb_set_page_with_attrs 0.86% -> 2.92%,
since a larger TLB costs more to fill and flush. So the softmmu lookup cost
(flatview_translate + find_memory_mapping, ~7.5%) is not driven by TLB
capacity. Reverted to the upstream default, with the refutation recorded in
place so nobody retries it without a new theory.
Also removes the temporary TLB probe.
Worth noting for future measurements: after the device was rebooted, the
same build measured ~33s where it had measured ~41s before. The earlier
drift was device state, not code.
Co-Authored-By: Claude <noreply@anthropic.com>