librelane playground

No. 119 / project of 147 on the ladder

LSU request scoreboard

introduces — shadow LSU request record; in-order scoreboard busy accounting; request lifetime counters

harden statelast run2026-05-06
signoff
  • DRCNOT RUN
  • LVSNOT RUN
  • antennaNOT RUN
artifacts

P119 adds a shadow LSU request record and scoreboard-style busy counter. It is intentionally observational: it does not let memory operations overtake commit or issue independently.

checkresult
Verilator buildPASS
BusyBox shell workload reaches P119-FILE-OKPASS
Request scoreboard counters emittedPASS
Hardened layoutNOT RUN
request countervalue
allocs27,889,983
completes27,749,744
flushes443
busy cycles30,685,198
scoreboard busy cycles30,685,198
valid at end0
metricP118P119
shell window cycles64,957,90464,930,511
S_FETCH cycles7,628,2207,630,872
S_MEM cycles27,758,93327,749,744

The alloc/complete mismatch is not treated as a bug in P119. It is the reason this rung exists: page-walk, trap, and retry paths need a tighter request lifetime definition before the record can become a real decoupled LSU interface.

shell phases label P119 shell workload cycles 218,814,345 cpi 2.53
  1. kernel banner to /init 116,715,634 53.5%
  2. /init to shell banner 1,074,202 0.5%
  3. shell banner to first command 35,465,931 16.3%
  4. echo command 1,649 0%
  5. uname -a 2,511,546 1.2%
  6. ls /bin /usr/share 31,849,963 14.6%
  7. cat sample file 2,687,768 1.2%
  8. touch/write/cat/rm /tmp file 11,362,750 5.2%
  9. 8x ash loop with file I/O 16,516,155 7.6%
  10. final marker 680 0%
state breakdown label P119 request scoreboard workload cycles 218,814,345 cpi 2.53
  1. fetch 3.5% 7,630,872
  2. execute 39.5% 86,389,835
  3. mem 12.8% 28,029,336
  4. walker 1.2% 2,690,983
  5. writeback 39.5% 86,364,977
  6. mul/div 3.5% 7,706,626