Remove CPU locking

This was already accidentally disabled in ba87b08. It also no longer
appears to be beneficial, and in fact slow things down, e.g. when
evaluating a NixOS system configuration:

  elapsed time:       median =      3.8170  mean =      3.8202  stddev =      0.0195  min =      3.7894  max =      3.8600  [rejected, p=0.00000, Δ=0.36929±0.02513]

5 files changed, 1 insertions, 87 deletions

diff --git a/src/libutil/affinity.cc b/src/libutil/affinity.cc
deleted file mode 100644
index ac2295e4a..000000000
--- a/src/libutil/affinity.cc
+++ /dev/null
@@ -1,70 +0,0 @@
-#include "types.hh"
-#include "util.hh"
-#include "affinity.hh"
-
-#if __linux__
-#include <sched.h>
-#endif
-
-namespace nix {
-
-
-#if __linux__
-static bool didSaveAffinity = false;
-static cpu_set_t savedAffinity;
-
-std::ostream& operator<<(std::ostream &os, const cpu_set_t &cset)
-{
-    auto count = CPU_COUNT(&cset);
-    for (int i=0; i < count; ++i)
-    {
-        os << (CPU_ISSET(i,&cset) ? "1" : "0");
-    }
-
-    return os;
-}
-#endif
-
-
-void setAffinityTo(int cpu)
-{
-#if __linux__
-    if (sched_getaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1) return;
-    didSaveAffinity = true;
-    debug(format("locking this thread to CPU %1%") % cpu);
-    cpu_set_t newAffinity;
-    CPU_ZERO(&newAffinity);
-    CPU_SET(cpu, &newAffinity);
-    if (sched_setaffinity(0, sizeof(cpu_set_t), &newAffinity) == -1)
-        printError("failed to lock thread to CPU %1%", cpu);
-#endif
-}
-
-
-int lockToCurrentCPU()
-{
-#if __linux__
-    int cpu = sched_getcpu();
-    if (cpu != -1) setAffinityTo(cpu);
-    return cpu;
-#else
-    return -1;
-#endif
-}
-
-
-void restoreAffinity()
-{
-#if __linux__
-    if (!didSaveAffinity) return;
-    if (sched_setaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1)
-    {
-        std::ostringstream oss;
-        oss << savedAffinity;
-        printError("failed to restore CPU affinity %1%", oss.str());
-    }
-#endif
-}
-
-
-}
diff --git a/src/libutil/affinity.hh b/src/libutil/affinity.hh
deleted file mode 100644
index c1bd28e13..000000000
--- a/src/libutil/affinity.hh
+++ /dev/null
@@ -1,9 +0,0 @@
-#pragma once
-
-namespace nix {
-
-void setAffinityTo(int cpu);
-int lockToCurrentCPU();
-void restoreAffinity();
-
-}
diff --git a/src/libutil/thread-pool.cc b/src/libutil/thread-pool.cc
index 857ee91f8..dc4067f1b 100644
--- a/src/libutil/thread-pool.cc
+++ b/src/libutil/thread-pool.cc
@@ -1,13 +1,10 @@
 #include "thread-pool.hh"
-#include "affinity.hh"
 
 namespace nix {
 
 ThreadPool::ThreadPool(size_t _maxThreads)
     : maxThreads(_maxThreads)
 {
-    restoreAffinity(); // FIXME
-
     if (!maxThreads) {
         maxThreads = std::thread::hardware_concurrency();
         if (!maxThreads) maxThreads = 1;
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 43fea1b1e..e18648557 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -1,5 +1,4 @@
 #include "util.hh"
-#include "affinity.hh"
 #include "sync.hh"
 #include "finally.hh"
 #include "serialise.hh"
@@ -1004,7 +1003,6 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
             if (options.dieWithParent && prctl(PR_SET_PDEATHSIG, SIGKILL) == -1)
                 throw SysError("setting death signal");
 #endif
-            restoreAffinity();
             fun();
         } catch (std::exception & e) {
             try {
@@ -1675,8 +1673,6 @@ void restoreProcessContext(bool restoreMounts)
         restoreMountNamespace();
     }
 
-    restoreAffinity();
-
     #if __linux__
     if (savedStackSize) {
         struct rlimit limit;
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 4cc043a84..d08f42826 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -300,7 +300,7 @@ void setStackSize(size_t stackSize);
 
 
 /* Restore the original inherited Unix process context (such as signal
-   masks, stack size, CPU affinity). */
+   masks, stack size). */
 void restoreProcessContext(bool restoreMounts = true);
 
 /* Save the current mount namespace. Ignored if called more than