From 5f485965c4db83b118e681111c90a529210153e4 Mon Sep 17 00:00:00 2001
From: Pushkar N Kulkarni <pushkar.nk@in.ibm.com>
Date: Mon, 17 Dec 2018 15:43:55 +0000
Subject: [PATCH] Initialize ELG with the number of affinitized cores

The MultiThreadedEventLoopGroup that runs the HTTPServer is initialized with all the available cores. On Linux, it could be instead initialised to the number of affinitized cores. If the number of affinitized cores is lesser than the `System.coreCount`, initializing the MultiThreadedEventLoopGroup with the later comes with a performance penalty.
---
 Package.swift                                 |  5 ++-
 Sources/CLinuxHelpers/ProcessorAffinity.c     | 40 +++++++++++++++++++
 .../CLinuxHelpers/include/ProcessorAffinity.h | 19 +++++++++
 Sources/KituraNet/HTTP/HTTPServer.swift       | 12 +++++-
 4 files changed, 73 insertions(+), 3 deletions(-)
 create mode 100644 Sources/CLinuxHelpers/ProcessorAffinity.c
 create mode 100644 Sources/CLinuxHelpers/include/ProcessorAffinity.h

diff --git a/Package.swift b/Package.swift
index e4159ca2..ed9ad1e7 100644
--- a/Package.swift
+++ b/Package.swift
@@ -36,9 +36,12 @@ let package = Package(
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.
         // Targets can depend on other targets in this package, and on products in packages which this package depends on.
+        .target(
+            name: "CLinuxHelpers",
+            dependencies: []),
         .target(
             name: "KituraNet",
-            dependencies: ["NIO", "NIOFoundationCompat", "NIOHTTP1", "NIOOpenSSL", "SSLService", "LoggerAPI", "NIOWebSocket"]),
+            dependencies: ["NIO", "NIOFoundationCompat", "NIOHTTP1", "NIOOpenSSL", "SSLService", "LoggerAPI", "NIOWebSocket", "CLinuxHelpers"]),
         .testTarget(
             name: "KituraNetTests",
             dependencies: ["KituraNet"]),
diff --git a/Sources/CLinuxHelpers/ProcessorAffinity.c b/Sources/CLinuxHelpers/ProcessorAffinity.c
new file mode 100644
index 00000000..259b2f5b
--- /dev/null
+++ b/Sources/CLinuxHelpers/ProcessorAffinity.c
@@ -0,0 +1,40 @@
+/*
+ * Copyright IBM Corporation 2018
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifdef __linux__
+
+#define _GNU_SOURCE
+#include <sched.h>
+#include <unistd.h>
+
+// Reference: https://stackoverflow.com/questions/10490756/how-to-use-sched-getaffinity-and-sched-setaffinity-in-linux-from-c
+int linux_sched_getaffinity() {
+    cpu_set_t mask;
+    long nproc, i, count = 0;
+
+    if (sched_getaffinity(0, sizeof(cpu_set_t), &mask) == -1) {
+        return -1;
+    } else {
+        nproc = sysconf(_SC_NPROCESSORS_ONLN);
+        for (i = 0; i < nproc; i++) {
+            if(CPU_ISSET(i, &mask))
+                count += 1;
+        }
+        return count;
+    }
+}
+
+#endif
diff --git a/Sources/CLinuxHelpers/include/ProcessorAffinity.h b/Sources/CLinuxHelpers/include/ProcessorAffinity.h
new file mode 100644
index 00000000..0a180b99
--- /dev/null
+++ b/Sources/CLinuxHelpers/include/ProcessorAffinity.h
@@ -0,0 +1,19 @@
+/*
+ * Copyright IBM Corporation 2018
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if __linux__
+int linux_sched_getaffinity();
+#endif
diff --git a/Sources/KituraNet/HTTP/HTTPServer.swift b/Sources/KituraNet/HTTP/HTTPServer.swift
index 4af87d51..a65c5584 100644
--- a/Sources/KituraNet/HTTP/HTTPServer.swift
+++ b/Sources/KituraNet/HTTP/HTTPServer.swift
@@ -21,6 +21,7 @@ import NIOOpenSSL
 import SSLService
 import LoggerAPI
 import NIOWebSocket
+import CLinuxHelpers
 
 /// An HTTP server that listens for connections on a socket.
 public class HTTPServer : Server {
@@ -66,11 +67,18 @@ public class HTTPServer : Server {
     private let maxPendingConnections = 100
 
     /// The event loop group on which the HTTP handler runs
-    let eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount)
+    private let eventLoopGroup: MultiThreadedEventLoopGroup
 
     private var ctx: ChannelHandlerContext?
 
-    public init() { }
+    public init() {
+#if os(Linux)
+        let numberOfCores = Int(linux_sched_getaffinity())
+        self.eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: numberOfCores > 0 ? numberOfCores : System.coreCount)
+#else
+        self.eventLoopGroup = MultiThreadedEventLoopGroup(numberOfThreads: System.coreCount)
+#endif
+    }
 
     /// SSL cert configs for handling client requests
     public var sslConfig: SSLService.Configuration? {