Re: [PATCH v5 3/5] read-cache: load cache entries on worker threads

>
> This patch helps address the CPU cost of loading the index by creating
> multiple threads to divide the work of loading and converting the cache
> entries across all available CPU cores.
>
> It accomplishes this by having the primary thread loop across the index file
> tracking the offset and (for V4 indexes) expanding the name. It creates a
> thread to process each block of entries as it comes to them.
>
> I used p0002-read-cache.sh to generate some performance data:
>
> Test w/100,000 files                Baseline         Parallel entries
> ---------------------------------------------------------------------------
> read_cache/discard_cache 1000 times 14.08(0.01+0.10) 9.72(0.03+0.06) -31.0%
>
> Test w/1,000,000 files              Baseline         Parallel entries
> ------------------------------------------------------------------------------
> read_cache/discard_cache 1000 times 202.95(0.01+0.07) 154.14(0.03+0.06) -24.1%