Utilize stackalloc and access static byte data directly #767

iamcarbon · 2022-02-13T22:37:04Z

Eliminates various allocations utilizing stackalloc
Utilizes special syntax to access static byte data directly (see Refer directly to static data when ReadOnlySpan wraps arrays of bytes. dotnet/roslyn#24621)

…a directly See dotnet/roslyn#24621 & https://vcsjones.dev/csharp-readonly-span-bytes-static/

iamcarbon · 2022-02-13T22:37:55Z

@jstedfast ready for review.

jstedfast · 2022-02-13T22:48:36Z

MimeKit/Header.cs

-			char[] chars = new char[count];
+			Span<char> chars = count < 16
+				? stackalloc char[16]
+				: new char[count];



Does using Span<> here really help?

Okay, so if my quick research is correct (don't have time for a full reading because I'm about to run out), I guess using Span<> with stackalloc removes the need to declare the method unsafe?

This is always a WIN when in throughput on .NET 5+ [we eliminate an allocation and avoid zeroing the stack], but there's a small penalty on older runtimes where we don't have SkipLocalsInit.

You are also right in that stackallocing into a Span is safe (otherwise, we deal with an unsafe pointer when using its natural type)

jstedfast · 2022-02-13T22:49:50Z

MimeKit/Header.cs

-			var chars = new char[fieldNameLength];
+			Span<char> chars = fieldNameLength <= 32
+				? stackalloc char[32]
+				: new char[fieldNameLength];


Same question about Span<>, but also why 32 here but 16 elsewhere?

I did some random checking to see the averages sizes and found them to be small or large (12 bytes or 100+ bytes). Standardizing on 32 bytes seems reasonable however.

jstedfast · 2022-02-13T22:50:07Z

MimeKit/Header.cs

@@ -312,9 +312,14 @@ protected Header (ParserOptions options, HeaderId id, string name, byte[] field,
 		/// <param name="fieldNameLength">The length of the field name (not including trailing whitespace).</param>
 		/// <param name="value">The raw value of the header.</param>
 		/// <param name="invalid"><c>true</c> if the header field is invalid; othereise, <c>false</c>.</param>
+#if NET5_0_OR_GREATER
+		[System.Runtime.CompilerServices.SkipLocalsInit]
+#endif


Not sure what this does...

Ah... https://www.meziantou.net/csharp-9-improve-performance-using-skiplocalsinit.htm

Yep. This is what gives us the win. It's basically free to use the stack if we use uncleared memory -- while avoiding the allocation.

jstedfast · 2022-02-13T22:54:53Z

MimeKit/Encodings/Base64Decoder.cs

@@ -37,7 +37,7 @@ namespace MimeKit.Encodings {
 	/// </remarks>
 	public class Base64Decoder : IMimeDecoder
 	{
-		static readonly byte[] base64_rank = new byte[256] {
+		static ReadOnlySpan<byte> base64_rank => new byte[256] {
 			255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,


should this be static readonly ReadOnlySpan<byte> ...? and why => vs =?

this is a really weird syntax that requires you to understand how Roslyn transforms it. It looks like it's allocating on every use, but Roslyn burns the data directly into the data file instead. This allows the code to access the data directly and eliminate various indirections and bounds checks.

jstedfast · 2022-02-13T22:59:21Z

Thanks for the link to https://vcsjones.dev/csharp-readonly-span-bytes-static/ in one of your commits. Very useful documentation.

jstedfast · 2022-02-13T23:00:45Z

MimeKit/Utils/MimeUtils.cs

@@ -508,6 +508,8 @@ public static string Quote (string text)
 			return Quote (text.AsSpan ());
 		}

+		private static readonly char[] unquoteChars = new[] { '\r', '\n', '\t', '\\', '"' };
+
 		/// <summary>


I prefer to define my "constants" at the top and using PascalCase.

jstedfast · 2022-02-14T02:18:19Z

Pre-merge:

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
.NET SDK=6.0.200
[Host] : .NET 5.0.14 (5.0.1422.5710), X64 RyuJIT [AttachedDebugger]
DefaultJob : .NET 5.0.14 (5.0.1422.5710), X64 RyuJIT

Method	Mean	Error	StdDev
Base64Decoder	420,581.7 ns	4,948.10 ns	4,628.46 ns
QuotedPrintableDecoder	848.7 ns	16.74 ns	25.05 ns
UUDecoder	606,899.6 ns	1,058.71 ns	884.07 ns

Method	Mean	Error	StdDev
Base64Encoder	254.2 us	2.62 us	2.46 us
HexEncoder	737.8 us	3.72 us	3.30 us
UUEncoder	213.3 us	1.00 us	0.88 us

Post-merge:

Method	Mean	Error	StdDev
Base64Decoder	415,734.2 ns	8,241.76 ns	19,746.72 ns
QuotedPrintableDecoder	840.8 ns	6.52 ns	6.10 ns
UUDecoder	564,594.0 ns	5,206.78 ns	4,615.67 ns

Method	Mean	Error	StdDev
Base64Encoder	208.0 us	1.14 us	1.06 us
HexEncoder	706.4 us	2.41 us	2.13 us
UUEncoder	213.4 us	0.87 us	0.77 us

jstedfast · 2022-02-14T02:26:01Z

Just for fun:

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
.NET SDK=6.0.200
[Host] : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT [AttachedDebugger]
DefaultJob : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT

Method	Mean	Error	StdDev
Base64Decoder	363,079.5 ns	4,604.11 ns	4,081.43 ns
QuotedPrintableDecoder	690.8 ns	12.53 ns	19.51 ns
UUDecoder	457,311.7 ns	2,263.63 ns	2,006.65 ns

Method	Mean	Error	StdDev
Base64Encoder	210.8 us	2.21 us	1.96 us
HexEncoder	630.1 us	3.45 us	3.06 us
UUEncoder	214.3 us	0.85 us	0.71 us

iamcarbon · 2022-02-14T02:30:33Z

Ahh, .NET6.0! ❤️

jstedfast · 2022-02-14T02:53:59Z

If you really want to be blown away:

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
[Host] : .NET Framework 4.8 (4.8.4420.0), X64 RyuJIT [AttachedDebugger]
DefaultJob : .NET Framework 4.8 (4.8.4420.0), X64 RyuJIT

Method	Mean	Error	StdDev	Median
MimeParser_StarTrekMessage	353.67 ms	6.933 ms	6.809 ms	353.74 ms
MimeParser_StarTrekMessagePersistent	262.98 ms	5.230 ms	6.800 ms	261.44 ms
MimeParser_ContentLengthMbox	32.55 ms	0.717 ms	2.104 ms	31.49 ms
MimeParser_ContentLengthMboxPersistent	26.94 ms	0.105 ms	0.087 ms	26.93 ms
MimeParser_JwzMbox	263.29 ms	3.201 ms	2.994 ms	263.95 ms
MimeParser_JwzMboxPersistent	211.77 ms	1.594 ms	1.491 ms	211.61 ms
MimeParser_HeaderStressTest	56.94 ms	0.393 ms	0.368 ms	56.78 ms
ExperimentalMimeParser_StarTrekMessage	333.69 ms	5.282 ms	4.940 ms	331.58 ms
ExperimentalMimeParser_StarTrekMessagePersistent	240.90 ms	1.865 ms	1.745 ms	241.26 ms
ExperimentalMimeParser_ContentLengthMbox	30.78 ms	0.190 ms	0.168 ms	30.75 ms
ExperimentalMimeParser_ContentLengthMboxPersistent	26.51 ms	0.129 ms	0.121 ms	26.53 ms
ExperimentalMimeParser_JwzMbox	258.84 ms	2.870 ms	2.544 ms	258.67 ms
ExperimentalMimeParser_JwzMboxPersistent	209.61 ms	1.351 ms	1.197 ms	209.75 ms
ExperimentalMimeParser_HeaderStressTest	52.84 ms	0.637 ms	0.532 ms	52.88 ms
MimeReader_StarTrekMessage	176.17 ms	0.984 ms	0.921 ms	176.26 ms
MimeReader_ContentLengthMbox	12.56 ms	0.036 ms	0.030 ms	12.57 ms
MimeReader_JwzMbox	130.99 ms	0.531 ms	0.497 ms	130.99 ms
MimeReader_HeaderStressTest	15.33 ms	0.130 ms	0.121 ms	15.35 ms

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
.NET SDK=6.0.200
[Host] : .NET 5.0.14 (5.0.1422.5710), X64 RyuJIT [AttachedDebugger]
DefaultJob : .NET 5.0.14 (5.0.1422.5710), X64 RyuJIT

Method	Mean	Error	StdDev	Median
MimeParser_StarTrekMessage	293.98 ms	4.907 ms	6.381 ms	293.48 ms
MimeParser_StarTrekMessagePersistent	231.20 ms	4.423 ms	11.574 ms	225.23 ms
MimeParser_ContentLengthMbox	26.45 ms	0.151 ms	0.134 ms	26.42 ms
MimeParser_ContentLengthMboxPersistent	22.94 ms	0.208 ms	0.184 ms	22.94 ms
MimeParser_JwzMbox	228.91 ms	1.944 ms	1.623 ms	228.72 ms
MimeParser_JwzMboxPersistent	191.09 ms	3.742 ms	3.500 ms	190.50 ms
MimeParser_HeaderStressTest	49.65 ms	0.784 ms	0.695 ms	49.33 ms
ExperimentalMimeParser_StarTrekMessage	270.28 ms	2.162 ms	2.022 ms	270.39 ms
ExperimentalMimeParser_StarTrekMessagePersistent	223.18 ms	1.491 ms	1.395 ms	223.41 ms
ExperimentalMimeParser_ContentLengthMbox	26.93 ms	0.404 ms	0.378 ms	26.98 ms
ExperimentalMimeParser_ContentLengthMboxPersistent	23.18 ms	0.377 ms	0.352 ms	23.08 ms
ExperimentalMimeParser_JwzMbox	233.51 ms	3.549 ms	5.629 ms	231.61 ms
ExperimentalMimeParser_JwzMboxPersistent	185.65 ms	1.778 ms	1.576 ms	185.33 ms
ExperimentalMimeParser_HeaderStressTest	41.11 ms	0.518 ms	0.485 ms	41.13 ms
MimeReader_StarTrekMessage	172.53 ms	3.328 ms	3.417 ms	171.93 ms
MimeReader_ContentLengthMbox	11.23 ms	0.045 ms	0.040 ms	11.25 ms
MimeReader_JwzMbox	122.64 ms	0.535 ms	0.501 ms	122.73 ms
MimeReader_HeaderStressTest	12.14 ms	0.118 ms	0.111 ms	12.13 ms

BenchmarkDotNet=v0.13.1, OS=Windows 10.0.22000
Intel Core i7-9700 CPU 3.00GHz, 1 CPU, 8 logical and 8 physical cores
.NET SDK=6.0.200
[Host] : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT [AttachedDebugger]
DefaultJob : .NET 6.0.2 (6.0.222.6406), X64 RyuJIT

Method	Mean	Error	StdDev	Median
MimeParser_StarTrekMessage	284.47 ms	3.984 ms	3.327 ms	284.93 ms
MimeParser_StarTrekMessagePersistent	221.08 ms	4.297 ms	9.959 ms	215.28 ms
MimeParser_ContentLengthMbox	25.78 ms	0.204 ms	0.181 ms	25.70 ms
MimeParser_ContentLengthMboxPersistent	21.96 ms	0.214 ms	0.200 ms	21.91 ms
MimeParser_JwzMbox	225.38 ms	1.505 ms	1.334 ms	225.36 ms
MimeParser_JwzMboxPersistent	181.97 ms	1.724 ms	1.613 ms	181.89 ms
MimeParser_HeaderStressTest	47.07 ms	0.421 ms	0.394 ms	47.02 ms
ExperimentalMimeParser_StarTrekMessage	264.82 ms	1.183 ms	1.107 ms	265.28 ms
ExperimentalMimeParser_StarTrekMessagePersistent	208.25 ms	1.522 ms	1.350 ms	208.46 ms
ExperimentalMimeParser_ContentLengthMbox	25.28 ms	0.179 ms	0.159 ms	25.27 ms
ExperimentalMimeParser_ContentLengthMboxPersistent	21.88 ms	0.164 ms	0.145 ms	21.89 ms
ExperimentalMimeParser_JwzMbox	225.96 ms	3.570 ms	3.339 ms	225.59 ms
ExperimentalMimeParser_JwzMboxPersistent	178.55 ms	1.198 ms	1.062 ms	178.42 ms
ExperimentalMimeParser_HeaderStressTest	38.61 ms	0.329 ms	0.308 ms	38.55 ms
MimeReader_StarTrekMessage	159.09 ms	0.728 ms	0.681 ms	159.18 ms
MimeReader_ContentLengthMbox	10.73 ms	0.082 ms	0.073 ms	10.73 ms
MimeReader_JwzMbox	118.88 ms	0.707 ms	0.591 ms	118.82 ms
MimeReader_HeaderStressTest	11.24 ms	0.062 ms	0.048 ms	11.24 ms

iamcarbon · 2022-02-14T03:02:09Z

Those are lovely performance improvements. Excited to see these improve even further on .NET7.0!

iamcarbon added 4 commits February 13, 2022 13:57

Eliminate array allocation in Unquote

5159e1e

Use stackalloc in Unfold to reduce string allocations

69f4313

Use stackalloc in Header constructor

a1aeace

Use static ReadOnly<byte> compiler feature to reference to static dat…

263a76e

…a directly See dotnet/roslyn#24621 & https://vcsjones.dev/csharp-readonly-span-bytes-static/

iamcarbon changed the title ~~Various improvements~~ Utilize stackalloc and access static byte data directly Feb 13, 2022

jstedfast reviewed Feb 13, 2022

View reviewed changes

iamcarbon added 3 commits February 13, 2022 15:11

Bump stackalloc threshold to 32 chars (64 bytes)

375837e

Move unquoteChars chars to top of file and fix casing

a4bca1d

Eliminate two buffer allocations in DecodeRfc2231

6e98397

jstedfast merged commit 045f5c0 into jstedfast:master Feb 14, 2022

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Utilize stackalloc and access static byte data directly #767

Utilize stackalloc and access static byte data directly #767

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Utilize stackalloc and access static byte data directly #767

Utilize stackalloc and access static byte data directly #767

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