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romanett 28f1401324 Server: cut request-path lock contention and allocation; add load harness (#4707)
Profiling the reference server under load showed most request-path CPU
spent spinning on contended locks, plus several avoidable allocations
per request or per node. This PR removes them, switches the reference
server to Server GC, and adds the load harness used to measure it.

## Results

Paired A/B against `master` (3 alternating rounds, medians, 20 sessions,
workstation GC on both sides, 24-core machine):

| Scenario | Throughput | p50 | p90 | Server CPU / op | Server alloc /
op | Lock contention |
|---|---|---|---|---|---|---|
| Read, 1 value | **+45%** (94k → 137k req/s) | −20% | −46% | −37% |
−39% | −94% |
| Read, 100 values | **+40%** | −26% | −17% | −24% | −25% | +130% ¹ |
| Read, 100 values, SignAndEncrypt | **+48%** | −36% | −20% | −30% |
−26% | +106% ¹ |
| Browse (Server object) | **+33%** | −31% | −12% | −13% | −14% | −40% |
| Write, 100 values | +13% | −12% | −4% | −10% | −19% | −23% |
| Data-change subscriptions | ±0 ² | ≈ | ≈ | −14% | −17% | −29% |

¹ The faster server spends more time in the remaining per-node locks.
² Throughput is bounded by the writer rate in this scenario.

Separately, Server GC instead of workstation GC doubles Read-100
throughput (21k → 44k req/s) and cuts p90 from 2.1 ms to 0.6 ms, because
workstation GC paused the server for about half the wall time under
load. The working set grows from ~210 MB to ~430 MB.

## Changes

- **`ObjectPool<T>`**: lock-free slot array. `ConcurrentBag.Count` took
every per-thread lock on each `Return` of the pooled response value-task
source, once per request.
- **`FairRequestQueue`**:
- drops redundant gate entries: the fail-fast pre-checks and the stopped
check read volatile fields and are re-checked under the gate; the owner
count is folded into selection;
- coalesces wake pulses with a pending flag, so the bounded signal
channel's lock is only taken when no token is outstanding. Wake-count
semantics in the tests are unchanged.
- **`DefaultServerResourceIsolationProvider`**:
  - compares peer addresses without `GetAddressBytes()` allocations;
- builds the unsecured verification context only when a classifier is
configured.
- **TCP listener / channel**: caches the certificate DER copies per
channel, keyed on the certificate instance. `X509Certificate2.RawData`
returns a fresh copy on every access, and the listener read it for every
request.
- **`EndpointBase`**: resolves the request `ActivitySource` once instead
of `Assembly.GetCallingAssembly()` per request.
- **Node managers**:
- one `ServerSystemContext` copy per request (cached on the
`OperationContext`) for per-node callbacks: permission metadata, node
metadata, view membership, method lookup;
  - removes a discarded copy in `GetReferenceDescriptionAsync`;
- per-request operation caches are plain `Dictionary` instead of a
`ConcurrentDictionary` with 24 lock objects;
  - the validation cache is built in one pass;
  - fixes zero-capacity error lists.
- **`ResourceManager`**: translation lookups read an immutable snapshot
that is rebuilt after writes. Browse serialised on the global lock for
every display name.
- **`MonitoredItem`**: shares the default `DataChangeFilter` instead of
allocating one per sampled value.
- **Reference server**: `ServerGarbageCollection=true`; new "Garbage
collector mode" section in `docs/ServerScalability.md`.
- **`perf/`**: `ServerLoadHarness` (out-of-process server plus load
driver, server-side CPU/GC/alloc/contention deltas, optional
`dotnet-trace` capture), `TraceAnalyzer` (TraceEvent-based
CPU/allocation/contention aggregation), and paired A/B scripts. Not part
of `UA.slnx`.

### Behaviour notes for custom node managers
- The `IDictionary<NodeId, NodeState>` operation cache handed to
overrides is now a `Dictionary`. It was a `ConcurrentDictionary`, but
only one request flow uses it.
- Within one request, per-node callbacks of a node manager share one
`ServerSystemContext` copy.

### Later commits on this PR
- **Permission checks without `NodeMetadata`** (`9068684c3`): the
role-permission and access-restriction validators run on an internal
`PermissionMetadata` struct; `AsyncCustomNodeManager` fills it on the
stack from the same attributes and namespace defaults. Browse's
reference filter reads 3 attributes per target instead of 13. Read 100
values: 120.6 → 95.7 KB/request, ~21k → 26k req/s; Browse 67.6 → 51.8
KB, 26.7k → 29.8k req/s.
- **Read-only channel evidence** (`936b28d76`, `dc638ab9f`):
`SecureChannelContext.ClientChannelCertificate`,
`ServerChannelCertificate` and `ChannelThumbprint` are `ByteString`, so
the cached per-channel certificate buffer is shared without a copy and
cannot be altered by handlers or classifiers. **Public API change**, see
the new section in `docs/MigrationGuide.md`. The isolation provider's
revalidation snapshot still copies.
- **Session lookup** (`936b28d76`):
`SessionManager.TryGetSessionContext` takes the candidate snapshot
without the bindings lock; the validating check under the lock is
unchanged (2 instead of 4 global lock acquisitions per request).
- Unit tests for `ObjectPool`, the per-request system context cache, the
translation snapshot, `SecureChannelContext` null semantics and a
stopped `FairRequestQueue`; `perf/` follows the repository conventions.

## Testing
- `Opc.Ua.Server.Tests` (net10.0): 8386 passed before the `ByteString`
change. After it, 13 secure-session and isolation tests failed; both
causes are fixed in `dc638ab9f` and those tests (25 with their variants)
pass. A full rerun of the Server, Sessions, Core, Redundancy, LDS and
GDS suites on the final commit is in progress.
- Full solution builds for net10.0 and net48; `dotnet format whitespace`
clean.

### o6-automation opcua-benchmarks (sampling, deep pipelines)
Replicated both tests of the [o6-automation
benchmark](https://github.com/o6-automation/opcua-benchmarks) in the
harness (`--scenario counters`, and `read` with 10 clients × N
outstanding), paired against `origin/master`:

| Test | master | this PR |
|---|---|---|
| Subscription sampling, 100 Hz, every item ≥ 99 % of samples, 1 item |
FAIL (75–94 %) | PASS (100 %) |
| same, 1024 items | FAIL (64–73 %) | PASS (99.9 %) |
| same, capacity | — | between 4096 and 6144 items (~410–520k samples/s)
|
| Read, 10 clients × 100 outstanding, None | stalls (0–1.7k req/s) |
121–131k req/s |
| Read, 10 clients × 100 outstanding, SignAndEncrypt | stalls (0 req/s)
| 89–91k req/s |
| Read, 10 clients × 1000 outstanding | channels faulted
(`BadTcpNotEnoughResources`) | 0 errors, ~45–54k req/s |

- **Fixed-rate sampling** (`30b769d13`): the sampling loop waited one
interval after each sample, adding timer overshoot and sampling time to
every cycle; samples now have absolute deadlines.
- **Async response send** (`cdac5c5ca`): `SendResponse` blocked
thread-pool workers on the channel gate; with many requests in flight
the receive loop that was handed the gate waited for a pool thread and
the channel stalled. The TCP, Kestrel TCP and WebSocket listeners now
use `SendResponseAsync`.
- **Backpressure instead of channel fault** (`191cd2ba7`): server
channels stop reading while more than 100 responses are queued and
resume at 50, instead of faulting the channel. Client channels keep
reading. At 10,000 outstanding requests throughput is ~50k req/s with or
without the limit engaged, so the remaining gap to the 100-per-client
case is not the backpressure.

## Not changed
- `SentMessageQueue` deep-clones every `NotificationMessage`. Retained
messages return their pooled payloads on acknowledgement while the
response copy may still be queued for send, and a client can acknowledge
a sequence number before receiving it; the clone keeps a recycled
payload from reaching another session's response. Removing it needs a
send-completion hook from the transport.
- Generated responses allocate a default `ResponseHeader` that is
replaced (~2-3 % of per-request allocation). Fixing it means making
structure fields of every generated type lazily initialized, a
generator-wide change to default values, equality and encoding.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
2026-10-09 13:00:49 +02:00

277 lines
11 KiB
C#

/* ========================================================================
* Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
*
* OPC Foundation MIT License 1.00
*
* Permission is hereby granted, free of charge, to any person
* obtaining a copy of this software and associated documentation
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* ======================================================================*/
// Trace analyzer for perf/ServerLoadHarness traces. Not part of the product; see perf/README.md.
// TraceAnalyzer cpu <trace> [top] [focus] : on-CPU samples (blocked leaf frames dropped)
// TraceAnalyzer alloc <trace> [top] [type] : GCAllocationTick bytes by type, first Opc.Ua frame, stacks
// TraceAnalyzer contention <trace> [top] : ContentionStart events by Opc.Ua stack
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using Microsoft.Diagnostics.Tracing;
using Microsoft.Diagnostics.Tracing.Etlx;
using Microsoft.Diagnostics.Tracing.Parsers.Clr;
namespace Opc.Ua.Perf.TraceAnalyzer
{
/// <summary>
/// Aggregates EventPipe traces recorded by the server load harness.
/// </summary>
public static class Program
{
/// <summary>
/// Leaf frames of threads that wait rather than run. The sampled thread-time
/// profile samples blocked threads too, so these are dropped to approximate CPU.
/// </summary>
private static readonly string[] s_blockedLeafFrames =
[
"LowLevelLifoSemaphore.Wait",
"WaitForSignal",
"WorkerThreadStart",
"IOCompletionPoller.Poll",
"WaitOneNoCheck",
"Thread.Sleep",
"PollGCWorker|70_0",
"WaitMultipleIgnoringSyncContext",
"Monitor.Wait",
"!?"
];
/// <summary>
/// Entry point.
/// </summary>
public static int Main(string[] args)
{
if (args.Length < 2)
{
Console.WriteLine("usage: TraceAnalyzer cpu|alloc|contention <trace> [top] [focus]");
return 1;
}
string mode = args[0];
int top = args.Length > 2 ? int.Parse(args[2], CultureInfo.InvariantCulture) : 40;
string? focus = args.Length > 3 ? args[3] : null;
string etlx = TraceLog.CreateFromEventPipeDataFile(
args[1], null, new TraceLogOptions { ContinueOnError = true });
using var log = new TraceLog(etlx);
switch (mode)
{
case "contention":
Contention(log, top);
break;
case "cpu":
Cpu(log, top, focus);
break;
default:
Allocations(log, top, focus);
break;
}
return 0;
}
private static void Contention(TraceLog log, int top)
{
var byStack = new Dictionary<string, double>(StringComparer.Ordinal);
double total = 0;
foreach (TraceEvent e in log.Events)
{
if (e.EventName?.StartsWith("Contention/Start", StringComparison.Ordinal) != true)
{
continue;
}
total++;
var chain = new List<string>();
for (TraceCallStack? f = e.CallStack(); f != null && chain.Count < 7; f = f.Caller)
{
string n = Short(Name(f));
if (IsOurs(n) || chain.Count == 0)
{
chain.Add(n);
}
}
Add(byStack, string.Join("\n ", chain), 1);
}
Console.WriteLine(FormattableString.Invariant($"contention events: {total}"));
Dump("stacks", byStack, total, top);
}
private static void Cpu(TraceLog log, int top, string? focus)
{
var exclusive = new Dictionary<string, double>(StringComparer.Ordinal);
var inclusive = new Dictionary<string, double>(StringComparer.Ordinal);
var firstOurs = new Dictionary<string, double>(StringComparer.Ordinal);
var callers = new Dictionary<string, double>(StringComparer.Ordinal);
double total = 0;
int all = 0;
foreach (TraceEvent e in log.Events)
{
if (e.ProviderName != "Microsoft-DotNETCore-SampleProfiler")
{
continue;
}
all++;
object? type = e.PayloadByName("Type");
if (type != null && Convert.ToInt32(type, CultureInfo.InvariantCulture) != 2)
{
// not running managed code
continue;
}
TraceCallStack? stack = e.CallStack();
if (stack == null)
{
continue;
}
string leaf = Short(Name(stack));
if (s_blockedLeafFrames.Any(b => leaf.EndsWith(b, StringComparison.Ordinal)))
{
continue;
}
total++;
Add(exclusive, leaf, 1);
var seen = new HashSet<string>(StringComparer.Ordinal);
bool gotOurs = false;
bool focusHit = false;
for (TraceCallStack? f = stack; f != null; f = f.Caller)
{
string n = Short(Name(f));
if (seen.Add(n))
{
Add(inclusive, n, 1);
}
if (!gotOurs && IsOurs(n))
{
gotOurs = true;
Add(firstOurs, n, 1);
}
if (focus != null && !focusHit && n.Contains(focus, StringComparison.Ordinal))
{
focusHit = true;
Add(callers, f.Caller != null ? Short(Name(f.Caller)) : "<root>", 1);
}
}
}
Console.WriteLine(FormattableString.Invariant($"samples: on-cpu={total} all={all}"));
Dump("exclusive", exclusive, total, top);
Dump("first Opc.Ua frame", firstOurs, total, top);
Dump(
"inclusive (Opc.Ua only)",
inclusive.Where(k => IsOurs(k.Key)).ToDictionary(k => k.Key, k => k.Value, StringComparer.Ordinal),
total,
top);
if (focus != null)
{
Dump("callers of " + focus, callers, total, top);
}
}
private static void Allocations(TraceLog log, int top, string? focus)
{
var byType = new Dictionary<string, double>(StringComparer.Ordinal);
var byFrame = new Dictionary<string, double>(StringComparer.Ordinal);
var byStack = new Dictionary<string, double>(StringComparer.Ordinal);
double total = 0;
foreach (TraceEvent e in log.Events)
{
if (e is not GCAllocationTickTraceData tick)
{
continue;
}
double amount = tick.AllocationAmount64;
total += amount;
string type = tick.TypeName ?? "?";
Add(byType, type, amount);
string frame = "?";
var chain = new List<string>();
for (TraceCallStack? f = e.CallStack(); f != null; f = f.Caller)
{
string n = Short(Name(f));
if (!IsOurs(n))
{
continue;
}
if (frame == "?")
{
frame = n;
}
if (chain.Count < 6 || (focus != null && chain.Count < 12))
{
chain.Add(n);
}
}
Add(byFrame, type + " <- " + frame, amount);
if (focus == null || type.Contains(focus, StringComparison.Ordinal))
{
Add(byStack, type + "\n " + string.Join("\n ", chain), amount);
}
}
Console.WriteLine(FormattableString.Invariant($"sampled alloc total: {total / 1048576:F1} MB"));
Dump("by type", byType, total, top);
Dump("by type <- first Opc.Ua frame", byFrame, total, top);
Dump("stacks", byStack, total, top / 2);
}
private static void Add(Dictionary<string, double> totals, string key, double amount)
{
totals[key] = totals.GetValueOrDefault(key) + amount;
}
private static void Dump(string title, Dictionary<string, double> totals, double total, int count)
{
Console.WriteLine("--- " + title);
foreach (KeyValuePair<string, double> kv in totals.OrderByDescending(k => k.Value).Take(count))
{
Console.WriteLine(FormattableString.Invariant($"{100.0 * kv.Value / total,6:F2}% {kv.Key}"));
}
}
private static string Name(TraceCallStack frame)
{
string name = frame.CodeAddress.FullMethodName;
return string.IsNullOrEmpty(name) ? frame.CodeAddress.ModuleName + "!?" : name;
}
private static string Short(string method)
{
int p = method.IndexOf('(', StringComparison.Ordinal);
return p > 0 ? method[..p] : method;
}
private static bool IsOurs(string method)
{
return method.StartsWith("Opc.Ua", StringComparison.Ordinal) ||
method.StartsWith("Quickstarts", StringComparison.Ordinal);
}
}
}