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Use our own Discard for testing #35

Merged
merged 1 commit into from
Oct 20, 2024
Merged

Use our own Discard for testing #35

merged 1 commit into from
Oct 20, 2024

Commits on Oct 19, 2024

  1. Use our own Discard for testing 

    Turns out that io.Discard is implementing ReadFrom using a small buffer
(8192), confusing our benchmarks. We copyBuffer with 1 MiB buffer, but
io.Discard is using its own 8 KiB buffer to do huge amount of tiny
reads. These tiny reads are extremely slow for reading compressed
clusters, since we have to read and decompress the same cluster multiple
times.

With this change qcow2 zlib performance is 4 times better - it it still
slow, but matches better the real performance.

Before:

    % go test -bench Read
    BenchmarkRead0p/qcow2-12          14      78238414 ns/op     3430.99 MB/s      1051160 B/op        39 allocs/op
    BenchmarkRead0p/qcow2_zlib-12     14      78577923 ns/op     3416.17 MB/s      1051733 B/op        39 allocs/op
    BenchmarkRead50p/qcow2-12         21      54889353 ns/op     4890.48 MB/s      1183231 B/op        45 allocs/op
    BenchmarkRead50p/qcow2_zlib-12     1    3466799292 ns/op       77.43 MB/s    736076536 B/op    178764 allocs/op
    BenchmarkRead100p/qcow2-12        38      30562127 ns/op     8783.27 MB/s      1182901 B/op        45 allocs/op
    BenchmarkRead100p/qcow2_zlib-12    1    6834526167 ns/op       39.28 MB/s   1471530256 B/op    357570 allocs/op

After:

    % go test -bench Read
    BenchmarkRead0p/qcow2-12          14      77515735 ns/op     3462.98 MB/s      1050518 B/op        39 allocs/op
    BenchmarkRead0p/qcow2_zlib-12     14      77823402 ns/op     3449.29 MB/s      1050504 B/op        39 allocs/op
    BenchmarkRead50p/qcow2-12         24      48812158 ns/op     5499.36 MB/s      1181856 B/op        45 allocs/op
    BenchmarkRead50p/qcow2_zlib-12     2     899659187 ns/op      298.37 MB/s    184996316 B/op     43247 allocs/op
    BenchmarkRead100p/qcow2-12        61      19306020 ns/op    13904.24 MB/s      1181854 B/op        45 allocs/op
    BenchmarkRead100p/qcow2_zlib-12    1    1732168542 ns/op      154.97 MB/s    368850952 B/op     86460 allocs/op

Signed-off-by: Nir Soffer <[email protected]>
    @nirs
    nirs committed Oct 19, 2024
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