Perf improvements for small or value-type POCOs

[steveharter]

For a TechEmPower benchmark which uses a one-property struct, this shows a ~1.2x serialization improvement during serialization.

Note a value-type (struct) POCO is not common and should only be used when there are very few properties -- instead a POCO should be a reference-type (class).

Fixes #36635

Summary of changes:

• Add a LRU cache before the dictionary access that returns the metadata for the root type being (de)serialized. This is the biggest savings for small POCOs; larger POCOs are not affected since the dictionary access becomes insignificant compared to the rest of the work. Also this LRU helps most when there is low concurrency (few threads) or the same type is being repeatedly (de)serialized.
• In internal code, pass the value types using in to avoid unnecessary copies. The more serializable properties a value-type contains, the bigger the savings.
• Optimize property writes to include the quotes and colon as suggested by @Tornhoof. This also allowed for some AggressiveInlining fast-path changes to since the code path is now internal and specific to this optimization.
• Other AggressiveInlining changes. Both added and removed. The crossgen size of STJ.dll is now 15K smaller (1071K to 1056K).
• Property lookup for cache misses (due to case-insensitivity or different property ordering across JSON payloads for a given Type) is faster since the length is now embedded into the ulong key avoiding calls to SequenceEquals() when the length is different. This doesn't affect the TechEmPower scenarios.
• Other smaller misc changes.

Click to expand for benchmarks

Note the items in the "Slower" section appear to be random differences on my machine.

Changes <= 2% are ignored.

summary:
better: 60, geomean: 1.081
worse: 6, geomean: 1.042
total diff: 66

Slower	diff/base	Base Median (ns)	Diff Median (ns)	Modality
System.Text.Json.Serialization.Tests.WriteJson.Serializ	1.06	399455.00	422447.04
System.Text.Json.Serialization.Tests.WriteJson.Serializ	1.05	415556.58	436781.25
System.Text.Json.Serialization.Tests.WriteJson.Serializ	1.04	421354.56	438918.92
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromUtf8Byte	1.04	60123.19	62395.95
System.Text.Json.Serialization.Tests.WriteJson<ImmutableDictionary<String, Strin	1.04	22739.64	23542.93
System.Text.Json.Serialization.Tests.WriteJson.Serializ	1.03	393763.91	405899.18

Faster	base/diff	Base Median (ns)	Diff Median (ns)	Modality
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromUtf8Bytes	1.27	110.28	86.93
System.Text.Json.Serialization.Tests.TechEmPower.SerializeWithCachedBufferAndWri	1.22	157.92	128.98
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes	1.21	136.89	112.73
System.Text.Json.Serialization.Tests.TechEmPower.SerializeWithCachedBuffer	1.20	168.65	140.95
System.Text.Json.Serialization.Tests.WriteJson<HashSet>.SerializeToUtf8B	1.19	6923.56	5839.37
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromString	1.18	153.13	130.14
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.16	151.17	129.87
System.Text.Json.Serialization.Tests.WriteJson.Seria	1.15	320.42	278.51
System.Text.Json.Serialization.Tests.ReadJson.Deseri	1.14	304.91	267.69
System.Text.Json.Serialization.Tests.ReadMissingAndCaseInsensitive.Cas	1.14	1303.16	1145.62
System.Text.Json.Serialization.Tests.WriteJson.Seria	1.13	237.91	209.73
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.12	576.65	514.93
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.12	188.54	168.38
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8By	1.12	316.44	282.72
System.Text.Json.Serialization.Tests.WriteJson.Seria	1.11	261.98	235.15
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.11	400.38	360.51
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.11	443.86	400.77
System.Text.Json.Serialization.Tests.ReadJson.Deseri	1.10	361.03	326.98
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStream	1.09	287.03	263.85
System.Text.Json.Serialization.Tests.WriteJson.Seria	1.08	436.69	403.47
System.Text.Json.Serialization.Tests.WriteJson.Serial	1.08	682.21	631.29
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.08	858.27	794.58
System.Text.Json.Serialization.Tests.ReadJson.Deseri	1.08	532.88	493.99
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes	1.08	400.49	371.56
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.08	348.29	323.17
System.Text.Json.Serialization.Tests.WriteJson.Serial	1.08	641.82	595.65
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromUtf8Byt	1.07	481.45	448.85
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromUtf	1.07	416.76	388.67
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectPropert	1.07	11685.38	10908.28
System.Text.Json.Serialization.Tests.ReadJson.Deseria	1.07	1536.53	1435.71
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromString	1.07	611.60	571.62
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.07	825.48	774.76
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectProperty	1.06	240.80	226.22
System.Text.Json.Serialization.Tests.WriteJson.Serial	1.06	851.35	805.19
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.05	11071.73	10494.79
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStream	1.05	798.38	760.46
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStr	1.05	29917.50	28523.15
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectProperty	1.05	965.81	921.32
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes	1.05	773.55	738.47
System.Text.Json.Serialization.Tests.WriteJson.SerializeObjectPr	1.05	497.30	474.84
System.Text.Json.Serialization.Tests.ReadJson.Deseriali	1.05	306043.34	292656.13
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStr	1.05	481.74	460.92
System.Text.Json.Serialization.Tests.ReadMissingAndCaseInsensitive.Mis	1.04	797.91	765.76
System.Text.Json.Serialization.Tests.WriteJson.Serial	1.04	751.29	721.58
System.Text.Json.Serialization.Tests.ReadJson<ImmutableSortedDictionary<String,	1.04	69278.46	66565.23
System.Text.Json.Serialization.Tests.WriteJson.SerializeToString	1.04	17390.87	16731.64
System.Text.Json.Serialization.Tests.ReadJson.Deseria	1.04	1067.42	1028.77
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStream	1.04	62911.90	60661.09
System.Text.Json.Serialization.Tests.ReadMissingAndCaseInsensitive.Bas	1.04	1191.68	1149.92
System.Text.Json.Serialization.Tests.WriteJson<ImmutableSortedDictionary<String,	1.04	16905.74	16313.72
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.04	10598.59	10235.46
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromString	1.03	63096.82	61013.44
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8Bytes	1.03	16751.03	16241.27
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromString	1.03	1176.87	1142.29
System.Text.Json.Serialization.Tests.WriteJson<HashSet>.SerializeToStrin	1.03	6308.08	6126.69
System.Text.Json.Serialization.Tests.ReadJson.Deseria	1.03	1154.10	1121.70
System.Text.Json.Serialization.Tests.ReadJson.DeserializeFromStr	1.03	693.37	674.69
System.Text.Json.Serialization.Tests.WriteJson.SerializeToUtf8By	1.03	15614.74	15212.41
System.Text.Json.Serialization.Tests.ReadMissingAndCaseInsensitive.Cas	1.03	1181.37	1152.01
System.Text.Json.Serialization.Tests.WriteJson.SerializeToStream	1.02	16290.03	15892.85

Click to expand for temporary TechEmpower benchmark

Summary: 1.22x faster (when using a cached buffer)

Before:

Method	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
SerializeWithCachedBuffer	169.0 ns	1.15 ns	1.08 ns	169.0 ns	167.2 ns	170.5 ns	0.0227	-	-	144 B
SerializeWithCachedBufferAndWriter	155.3 ns	1.19 ns	1.11 ns	155.5 ns	153.3 ns	157.3 ns	0.0038	-	-	24 B
SerializeWithManualCode	116.4 ns	0.57 ns	0.48 ns	116.5 ns	115.6 ns	117.2 ns	0.0188	-	-	120 B

After:

Method	Mean	Error	StdDev	Median	Min	Max	Gen 0	Gen 1	Gen 2	Allocated
SerializeWithCachedBuffer	141.6 ns	2.33 ns	2.18 ns	141.2 ns	138.0 ns	144.8 ns	0.0227	-	-	144 B
SerializeWithCachedBufferAndWriter	130.8 ns	1.50 ns	1.40 ns	130.9 ns	128.6 ns	133.0 ns	0.0037	-	-	24 B
SerializeWithManualCode	112.1 ns	1.14 ns	1.07 ns	112.4 ns	110.5 ns	113.7 ns	0.0188	-	-	120 B

Code:

using BenchmarkDotNet.Attributes;
using MicroBenchmarks;
using System.Buffers;
using System.Threading.Tasks;

namespace System.Text.Json.Serialization.Tests
{
    public struct JsonMessage
    {
        public string message { get; set; }
    }

    public class TechEmPower
    {
        private static readonly JsonSerializerOptions SerializerOptions = new JsonSerializerOptions();

        ArrayBufferWriter<byte> _bufferWriter = new ArrayBufferWriter<byte>(160 * 16);
        Utf8JsonWriter _utf8Jsonwriter;


        [GlobalSetup]
        public void Setup()
        {
            _utf8Jsonwriter = new Utf8JsonWriter(_bufferWriter, new JsonWriterOptions { SkipValidation = true });
        }

        [BenchmarkCategory(Categories.Libraries, Categories.JSON)]
        [Benchmark]
        public void SerializeWithCachedBuffer()
        {
            _bufferWriter.Clear();
            var utf8JsonWriter = new Utf8JsonWriter(_bufferWriter, new JsonWriterOptions { SkipValidation = true });
            JsonSerializer.Serialize<JsonMessage>(utf8JsonWriter, new JsonMessage { message = "Hello, World!" }, SerializerOptions);
        }

        [BenchmarkCategory(Categories.Libraries, Categories.JSON)]
        [Benchmark]
        public void SerializeWithCachedBufferAndWriter()
        {
            _bufferWriter.Clear();
            JsonSerializer.Serialize<JsonMessage>(_utf8Jsonwriter, new JsonMessage { message = "Hello, World!" }, SerializerOptions);
        }

        [BenchmarkCategory(Categories.Libraries, Categories.JSON)]
        [Benchmark]
        public void SerializeWithManualCode()
        {
            _bufferWriter.Clear();
            using (var utf8JsonWriter = new Utf8JsonWriter(_bufferWriter))
            {
                var message = new JsonMessage { message = "Hello, World!" };
                utf8JsonWriter.WriteStartObject();
                utf8JsonWriter.WriteString("message", message.message);
                utf8JsonWriter.WriteEndObject();
            }
        }
    }
}

[steveharter]

Note this is for consistency with other code. Also applies to another case of this later.

[steveharter]

Note that GetPropertyName is marked with AggressiveInline but LookupProperty is not (it used to be, but there became 4 references to it over time causing code bloat).

[steveharter]

Changed this for readability (and to make short-circuiting of || obvious).

[layomia]

LGTM

[adamsitnik]

@stephentoub Please excuse me for not providing the code review on time.

@steveharter The numbers look really good! Thank you for sharing all the benchmark results!