4 ms·

Go allocations aren't that bad. A few years ago I benchmarked them at about 4x as expensive as a bump allocation. That is slow enough to make an arena beneficia

Go allocations aren't that bad. A few years ago I benchmarked them at about 4x as expensive as a bump allocation. That is slow enough to make an arena beneficial in high allocation situations, but fast enough to not make it worth it most of the time.

aktau 2y ago
Comparing with a fairly optimized malloc at $COMPANY, the Go allocator is (both in terms of relative cycles and fraction of cycles of all Go programs) significantly more expensive than the C/C++ counterpart (3-4x IIRC). For one, it has to do more work, like setting up GC metadata, and zeroing. There have recently been some optimizations to `runtime.mallocgc`, which may have decrease that 3-4x estimate a bit.
- nu11ptr 2y ago
  How can that be true? If it is 3-4x more expensive than malloc, then per my measurements your malloc is a bump allocator, and that simply isn't true for any real world malloc implementation (typically a modified free list allocator afaik). `mallocgc` may not be fast, but I simply did not find it as slow as you are saying. My guess is it is about as fast as most decent malloc functions, but I have not measured, and it would be interesting to see a comparison (tough to do as you'd need to call malloc via CGo or write one in C and one in Go and trust the looping is roughly the same cost).
  - aktau 2y ago
    I should correct and clarify: I meant 3-4x more expensive in relative terms. Meaning: - For C++ programs, the allocator (allocating+freeing) consumes roughly 5% of cycles. - For Go programs, the allocator (runtime.mallocgc) used to consume ~20% of cycles (this is the data I referenced). I checked and recently it's become closer to 15%, thanks to optimizations. I have not tested the performance differential on a per-byte level (though that will also differ with object structure in Go).

4 ms·

Go allocations aren't that bad. A few years ago I benchmarked them at about 4x as expensive as a bump allocation. That is slow enough to make an arena beneficia

by nu11ptr 2y ago

aktau 2y ago
Comparing with a fairly optimized malloc at $COMPANY, the Go allocator is (both in terms of relative cycles and fraction of cycles of all Go programs) significantly more expensive than the C/C++ counterpart (3-4x IIRC). For one, it has to do more work, like setting up GC metadata, and zeroing. There have recently been some optimizations to `runtime.mallocgc`, which may have decrease that 3-4x estimate a bit.
- nu11ptr 2y ago
  How can that be true? If it is 3-4x more expensive than malloc, then per my measurements your malloc is a bump allocator, and that simply isn't true for any real world malloc implementation (typically a modified free list allocator afaik). `mallocgc` may not be fast, but I simply did not find it as slow as you are saying. My guess is it is about as fast as most decent malloc functions, but I have not measured, and it would be interesting to see a comparison (tough to do as you'd need to call malloc via CGo or write one in C and one in Go and trust the looping is roughly the same cost).
  - aktau 2y ago
    I should correct and clarify: I meant 3-4x more expensive in relative terms. Meaning: - For C++ programs, the allocator (allocating+freeing) consumes roughly 5% of cycles. - For Go programs, the allocator (runtime.mallocgc) used to consume ~20% of cycles (this is the data I referenced). I checked and recently it's become closer to 15%, thanks to optimizations. I have not tested the performance differential on a per-byte level (though that will also differ with object structure in Go).