CopyBuffer allocates a 32k buffer when no buffer is available.
Allocate these buffers from a sync.Pool.
This removes an optimization where the copy buffer size was
reduced when the source is a io.LimitedReader (including the
case of CopyN) with a limit less than the default buffer size.
This change could cause a program which only uses io.Copy
with sources with a small limit to allocate unnecessarily
large buffers. Programs which care about the transient
buffer allocation can avoid this by providing their own buffer.
name old time/op new time/op delta
CopyNSmall-10 165ns ± 7% 117ns ± 7% -29.19% (p=0.001 n=7+7)
CopyNLarge-10 7.33µs ±34% 4.07µs ± 2% -44.52% (p=0.001 n=7+7)
name old alloc/op new alloc/op delta
CopyNSmall-10 2.20kB ±12% 1.20kB ± 4% -45.24% (p=0.000 n=8+7)
CopyNLarge-10 148kB ± 9% 81kB ± 4% -45.26% (p=0.000 n=8+7)
name old allocs/op new allocs/op delta
CopyNSmall-10 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.000 n=8+8)
CopyNLarge-10 2.00 ± 0% 1.00 ± 0% -50.00% (p=0.000 n=8+8)
For #57202
Change-Id: I2292226da9ba1dc09a2543f5d74fe5da06080d49
Reviewed-on: https://go-review.googlesource.com/c/go/+/456555
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com> Reviewed-by: Thomas Austad <thomas.austad@gmail.com>
Auto-Submit: Damien Neil <dneil@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>