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LibAudio: Avoid frequent read() calls in FLAC residual decode

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Decoding the residual in FLAC subframes is by far the most I/O-heavy
operation in FLAC decoding, as the residual data makes up the majority
of subframe data in LPC subframes. As the residual consists of many
Rice-encoded numbers with different bit sizes for differently large
numbers, the residual decoder frequently reads only one or two bytes at
a time. As we use a normal FileInputStream, that directly translates to
many calls to the read() syscall. We can see that the I/O overhead while
FLAC decoding is quite large, and much time is spent in the read()
syscall's kernel code.

This is optimized by using a Buffered<FileInputStream> instead, leading
to 4K blocks being read at once and a large reduction in I/O overhead.

Benchmarking with the new abench utility gives a 15-20% speedup on
identical files, usually pushing FLAC decoding to 10-15x realtime speed
on common sample rates.
This commit is contained in:
kleines Filmröllchen 2021-10-03 11:39:17 +02:00 • committed by Brian Gianforcaro
parent cbb2b4fe71
commit 14d330faba
2 changed files with 16 additions and 7 deletions
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12
Userland/Libraries/LibAudio/FlacLoader.h
View file

@ -10,6 +10,7 @@
#include "FlacTypes.h"
#include "Loader.h"
#include <AK/BitStream.h>
#include <AK/Buffered.h>
#include <AK/Stream.h>
#include <AK/Types.h>
#include <AK/Variant.h>
@ -17,16 +18,19 @@
namespace Audio {
class FlacInputStream : public Variant<Core::InputFileStream, InputMemoryStream> {
class FlacInputStream : public Variant<Buffered<Core::InputFileStream>, InputMemoryStream> {
public:
using Variant<Core::InputFileStream, InputMemoryStream>::Variant;
using Variant<Buffered<Core::InputFileStream>, InputMemoryStream>::Variant;
bool seek(size_t pos)
{
return this->visit(
[&](Core::InputFileStream& stream) {
return stream.seek(pos);
[&](Buffered<Core::InputFileStream>& buffered) {
// Discard the buffer, then seek normally.
if (!buffered.discard_or_error(buffered.buffered()))
return false;
return buffered.underlying_stream().seek(pos);
},
[&](InputMemoryStream& stream) {
if (pos >= stream.bytes().size()) {