Re: [PATCH 16/15] Add tracing to measure where most of the time is spent

> All the known heavy code blocks are measured (except object database
> access). This should help identify if an optimization is effective or
> not. An unoptimized git-status would give something like below (92% of
> time is accounted). To sum up the effort of making git scale better:
> 
>  - read cache line is being addressed by index-helper
>  - preload/refresh index by watchman
>  - read packed refs by lmdb backend
>  - diff-index by rebuilding cache-tree
>  - read directory by untracked cache and watchman
>  - write index by split index
>  - name hash potientially by index-helper
> 
> read-cache.c:2075         performance: 0.004058570 s: read cache .../index
> preload-index.c:104       performance: 0.004419864 s: preload index
> read-cache.c:1265         performance: 0.000185224 s: refresh index
> refs/files-backend.c:1100 performance: 0.001935788 s: read packed refs
> diff-lib.c:240            performance: 0.000144132 s: diff-files
> diff-lib.c:506            performance: 0.013592000 s: diff-index
> name-hash.c:128           performance: 0.000614177 s: initialize name hash
> dir.c:2030                performance: 0.015814103 s: read directory
> read-cache.c:2565         performance: 0.004052343 s: write index, changed mask = 2
> trace.c:420               performance: 0.048365509 s: git command: './git' 'status'