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_remote_debugging: Stop reading the base frame sentinel on every sample_remote_debugging: Stop reading the base frame sentinel
_remote_debugging: Stop reading the base frame sentinel_remote_debugging: Stop rereading the base frame sentinel
maurycy
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Oct 10, 2026
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+329
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+330
| if (frame_addr == ctx->base_frame_addr | ||
| && !(unwinder->gc && frame_addr == ctx->gc_frame)) { |
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| if (frame_addr == ctx->base_frame_addr | |
| && !(unwinder->gc && frame_addr == ctx->gc_frame)) { | |
| // Skip the base frame sentinel unless we need to emit a <GC> marker | |
| // because GC started with no Python frames on this thread. | |
| if (frame_addr == ctx->base_frame_addr | |
| && !(unwinder->gc && frame_addr == ctx->gc_frame)) { |
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Basically,
process_frame_chain()reads frames untilpreviousisNULL:cpython/Modules/_remote_debugging/frames.c
Lines 345 to 348 in 565f76f
The last one is always
tstate->base_framethat is the sentinel set up once per thread withprevious == NULLandowner == FRAME_OWNED_BY_INTERPRETER:cpython/Python/pystate.c
Lines 1589 to 1599 in 565f76f
Its address is already in the thread state buffer:
cpython/Modules/_remote_debugging/threads.c
Line 535 in 565f76f
so the remote read is not needed.
Tools/inspection/oracle_external_inspection.pywith--runs 3, PGO+LTO, Ubuntu 24.04, AMD EPYC 4484PX,mainat 182f323 vs the PR, on the same box one after another:182f323)182f323+ patchI'm not exactly sure why
basicordeep_staticare worse here. My guess it's just PGO noise.main (`182f323`)
PR (`182f323` + patch)
maurycy@taut cpython-B (182f323*) % ./python ./Tools/inspection/oracle_external_inspection.py --runs 3 3.16.0a0 (tags/v3.15.0b1-2187-g182f323154-dirty:182f323154, Oct 10 2026, 14:15:59) [GCC 13.3.0] cases=async_running_task,asyncio,basic,code_object_reuse,deep_recursion,deep_static,flat_alternating,gen_alternating,nested_alternating,oversized_chunk,shared_leaf,threads runs=3 duration=3.0 rate_khz=100.0 warmup=0.7 poisson_sampling=False async_running_task (get_async_stack_trace) ref_keys=46 mode samples stacks empty µs errors% impossible impossible% blocking-nocache 348511 697022 3379 23.11±0.11 0.00±0.00 0 0.00±0.00 live-nocache 460515 921009 3251 16.70±0.05 1.92±0.17 14318 1.56±0.31 asyncio (get_async_stack_trace) ref_keys=95 mode samples stacks empty µs errors% blocking-nocache 443576 553293 1683 18.90±0.10 0.00±0.00 live-nocache 594948 700929 2211 13.79±0.52 0.40±0.04 basic (get_stack_trace) ref_keys=32 mode samples µs errors% raw_tvd tvd_excess tvd_floor blocking-nocache 504897 16.63±0.03 0.00±0.00 ref ref - blocking-cache 617583 13.39±0.14 0.00±0.00 0.001±0.000 0.001±0.000 0.000 live-cache 899992 3.28±0.05 0.00±0.00 0.012±0.000 0.012±0.000 0.000 live-nocache 899995 6.05±0.05 0.00±0.00 0.013±0.000 0.013±0.000 0.000 code_object_reuse (get_stack_trace) ref_keys=22 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 620199 12.81±0.22 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 767626 10.07±0.25 0.00±0.00 0 0.00±0.00 0.001±0.000 -0.001±0.000 0.001 live-cache 899994 3.47±0.06 0.00±0.00 0 0.00±0.00 0.349±0.025 0.347±0.025 0.001 live-nocache 899991 6.36±0.01 0.00±0.00 0 0.00±0.00 0.005±0.000 0.004±0.000 0.001 deep_recursion (get_stack_trace) ref_keys=769 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 228284 18.90±0.24 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 220124 20.12±0.41 0.00±0.00 0 0.00±0.00 0.036±0.010 0.020±0.010 0.016 live-cache 83004 71.18±6.10 25.86±5.92 31325 38.01±2.84 0.693±0.046 0.666±0.048 0.028 live-nocache 192223 28.96±16.09 7.58±3.68 16518 9.73±6.10 0.850±0.019 0.832±0.017 0.017 deep_static (get_stack_trace) ref_keys=1 mode samples µs errors% raw_tvd tvd_excess tvd_floor blocking-nocache 56808 42.14±2.09 0.00±0.00 ref ref - blocking-cache 65545 17.24±0.94 0.00±0.00 0.000±0.000 0.000±0.000 0.000 live-cache 76141 5.82±0.08 0.00±0.00 0.000±0.000 0.000±0.000 0.000 live-nocache 63351 29.29±0.17 0.00±0.00 0.000±0.000 0.000±0.000 0.000 flat_alternating (get_stack_trace) ref_keys=6 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 614231 12.92±0.03 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 582285 13.73±0.02 0.00±0.00 0 0.00±0.00 0.024±0.005 0.021±0.005 0.002 live-cache 899991 7.13±0.02 0.00±0.00 4204 0.47±0.14 0.077±0.013 0.076±0.013 0.002 live-nocache 899999 6.37±0.01 0.00±0.00 5548 0.62±0.04 0.111±0.017 0.110±0.017 0.002 gen_alternating (get_stack_trace) ref_keys=19 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 590747 13.84±0.05 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 573287 14.31±0.09 0.00±0.00 0 0.00±0.00 0.036±0.011 0.032±0.011 0.004 live-cache 724332 7.36±0.03 19.52±0.68 154090 21.29±4.24 0.287±0.025 0.283±0.025 0.004 live-nocache 725428 7.02±0.03 19.40±0.96 372262 51.34±4.62 0.638±0.059 0.633±0.059 0.005 nested_alternating (get_stack_trace) ref_keys=12 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 584517 13.01±0.01 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 714155 10.23±0.03 0.00±0.00 0 0.00±0.00 0.030±0.006 0.028±0.006 0.002 live-cache 899992 3.65±0.01 0.00±0.00 30 0.00±0.01 0.037±0.040 0.035±0.040 0.002 live-nocache 899998 6.47±0.09 0.00±0.00 4 0.00±0.00 0.067±0.030 0.065±0.030 0.002 oversized_chunk (get_stack_trace) ref_keys=17 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 608009 13.03±0.04 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 714629 10.83±0.09 0.00±0.00 0 0.00±0.00 0.024±0.011 0.021±0.011 0.002 live-cache 899993 4.59±0.01 0.00±0.00 24505 2.72±0.28 0.066±0.013 0.064±0.013 0.002 live-nocache 899989 6.52±0.01 0.00±0.00 1 0.00±0.00 0.095±0.010 0.092±0.010 0.002 shared_leaf (get_stack_trace) ref_keys=10 mode samples µs errors% impossible impossible% raw_tvd tvd_excess tvd_floor blocking-nocache 617170 12.96±0.02 0.00±0.00 0 0.00±0.00 ref ref - blocking-cache 767359 10.12±0.02 0.00±0.00 0 0.00±0.00 0.032±0.024 0.031±0.024 0.001 live-cache 899993 3.52±0.01 0.00±0.00 685 0.08±0.06 0.071±0.047 0.070±0.047 0.001 live-nocache 899991 6.35±0.01 0.00±0.00 0 0.00±0.00 0.063±0.006 0.062±0.006 0.001 threads (get_stack_trace) ref_keys=8 mode samples stacks µs errors% raw_tvd tvd_excess tvd_floor blocking-nocache 62150 576377 159.09±86.15 0.00±0.00 ref ref - blocking-cache 76231 810134 113.85±35.56 0.00±0.00 0.035±0.037 0.034±0.037 0.001 live-cache 318426 2714810 19.70±2.44 0.00±0.00 0.042±0.017 0.041±0.017 0.001 live-nocache 127896 1394382 60.32±9.68 0.00±0.00 0.064±0.023 0.063±0.022 0.001_remote_debugging: reading whole pages over and over #149584