perf report --sort tid is not a valid sort key; use --sort pid to split samples per thread

On linux-tools 7.0 (Ubuntu 24.04 AWS kernel), perf report --sort tid does not error loudly in a scripted pipeline; it produces an empty report, so a per-thread breakdown file came out empty while the perf.data was fine. The working key is pid, which prints tid:comm per thread (each thread is its own task id). For exact per-thread totals use perf report --sort pid -g none --stdio | head -40; with call graphs on, the percentages include children and are harder to sum.

Lessons: - Check the report content (non-empty, has the expected thread names) before deleting perf.data, not just that the file exists. - Shares from perf are shares of samples, not CPU-seconds; label them that way and get CPU-s from getrusage or /usr/bin/time of the whole process tree.