stop allocating on every byte read (for CIDs and varints) #220
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We need a ByteReader for some APIs, such as reading CIDs.
However, our entrypoints often don't, such as Reader or ReaderAt.
Thus, we have a type that does the wrapping to support ReadByte.
We were converting a non-pointer to an interface,
which forcibly allocates, since interfaces must contain pointers.
Fix that by making the ReadByte methods use pointer receivers.
name old time/op new time/op delta
ReadBlocks-16 1.18ms ± 2% 1.15ms ± 5% -2.73% (p=0.003 n=11+11)
name old speed new speed delta
ReadBlocks-16 441MB/s ± 2% 453MB/s ± 5% +2.85% (p=0.003 n=11+11)
name old alloc/op new alloc/op delta
ReadBlocks-16 1.33MB ± 0% 1.29MB ± 0% -2.41% (p=0.000 n=12+12)
name old allocs/op new allocs/op delta
ReadBlocks-16 13.5k ± 0% 11.5k ± 0% -14.79% (p=0.000 n=12+12)
Like the last commit, avoid an extra allocation per read byte.
In this case, we created a one-byte buffer for each readByte call.
Unfortunately, since io.Reader is an interface,
the compiler can't know if it holds onto the memory,
so the buffer escapes and cannot be placed in the stack.
To sidestep this issue, reuse a preallocated buffer.
We know this is fine, because we only do sequential reads.
name old time/op new time/op delta
ReadBlocks-16 1.15ms ± 5% 1.09ms ± 4% -5.13% (p=0.000 n=11+11)
name old speed new speed delta
ReadBlocks-16 453MB/s ± 5% 478MB/s ± 4% +5.41% (p=0.000 n=11+11)
name old alloc/op new alloc/op delta
ReadBlocks-16 1.29MB ± 0% 1.30MB ± 0% +0.48% (p=0.000 n=12+12)
name old allocs/op new allocs/op delta
ReadBlocks-16 11.5k ± 0% 9.5k ± 0% -17.35% (p=0.000 n=12+12)
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(see commit messages - please do not squash)
Using ReadBlocks as an example, we have 30% fewer allocs and 7% less cpu usage.
ipfs/go-cid#132 does another 11% and 3%, respectively.