[PATCH] D119784: [Symbolize] LRU cache binaries in llvm-symbolizer.

[Daniel Thornburgh via Phabricator via llvm-commits]

mysterymath added a comment.

> Do you have some performance numbers? What if we didn't cache/had a cache size of 0? (does the caching logic buy us enough performance to justify it)

I did some poking around, and it looks like restarting the job after every request was tried as a workaround.
This choked on large binaries, and they had to change to restart-every-n requests.

I took a large debug binary, Clang, and symbolized 100 random symbols from it.

Zero-size LRU:

  real    4m44.289s
  user    4m27.506s
  sys     0m16.720s

No LRU, flush after each request:

  real    4m41.313s
  user    4m24.575s
  sys     0m16.666s

Unbounded LRU:

  real    0m4.309s
  user    0m3.842s
  sys     0m0.471s

HEAD:

  real    0m4.505s
  user    0m3.982s
  sys     0m0.526s

Conversely, we can look at how much overhead the LRU order maintenance adds to 100000 very easily cacheable requests (lookup `main` in `int main(void){return 0;}`).

Unbounded LRU:

  real    0m0.421s
  user    0m0.305s
  sys     0m0.120s

HEAD:

  real    0m0.410s
  user    0m0.334s
  sys     0m0.079s

Looking at the zero-size LRU, I think we'd probably want cache sizes to be soft.
If a large binary is symbolized, and the binary is over the cap, then it's guaranteed to be evicted from the cache after each request, even though this doesn't lower the peak memory usage of the binary.
Instead, we can inflate the cap to the size of the largest individual binary that has been symbolized; this is the high water mark of memory usage overall.
This would let us pick a relatively low default cap, say 500MiB, without harming performance when symbolizing larger binaries.

Also, I realize that these examples are synthetic, but they should help characterize the edge case behaviors at least.  I'll post back with a real example from system logs soon.


Repository:
  rG LLVM Github Monorepo

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