tree bbb2df9c35bc906d1916e1b80575e1d959a5846c
parent 3b3adefd58826ca4dfd87df8099766d416c54341
author Amir Ayupov <aaupov@fb.com> 1747167613 -0700
committer GitHub <noreply@github.com> 1747167613 -0700
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[BOLT][heatmap] Compute section utilization and partition score (#139193)

Heatmap groups samples into buckets of configurable size (`--block-size`
flag with 64 bytes as the default =X86 cache line size). Buckets are
mapped to containing sections; for buckets that cover multiple sections,
they are attributed to the first overlapping section. Buckets not mapped
to a section are reported as unmapped.

Heatmap reports **section hotness** which is a percentage of samples
attributed to the section.

Define **section utilization** as a percentage of buckets with non-zero
samples relative to the total number of section buckets.

Also define section **partition score** as a product of section hotness
(where total excludes unmapped buckets) and mapped utilization, ranging 
from 0 to 1 (higher is better).

The intended use of new metrics is with **production profile** collected
from BOLT-optimized binary. In this case the partition score of .text
(hot text if function splitting is enabled) reflects **optimization
profile** representativeness and the quality of hot-cold splitting.
Partition score of 1 means that all samples fall into hot text, and all
buckets (cache lines) in hot text are exercised, equivalent to perfect
hot-cold splitting.

Test Plan: updated heatmap-preagg.test