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Run the daemon worker on the same CPU as the client

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On a system with multiple CPUs, running Nix operations through the
daemon is significantly slower than "direct" mode:

$ NIX_REMOTE= nix-instantiate '<nixos>' -A system
real    0m0.974s
user    0m0.875s
sys     0m0.088s

$ NIX_REMOTE=daemon nix-instantiate '<nixos>' -A system
real    0m2.118s
user    0m1.463s
sys     0m0.218s

The main reason seems to be that the client and the worker get moved
to a different CPU after every call to the worker.  This patch adds a
hack to lock them to the same CPU.  With this, the overhead of going
through the daemon is very small:

$ NIX_REMOTE=daemon nix-instantiate '<nixos>' -A system
real    0m1.074s
user    0m0.809s
sys     0m0.098s
This commit is contained in:
Eelco Dolstra 2013-08-07 11:51:55 +00:00
parent 263d668222
commit a583a2bc59
9 changed files with 92 additions and 4 deletions
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54
src/libutil/affinity.cc Normal file
View file

@ -0,0 +1,54 @@
#include "types.hh"
#include "util.hh"
#include "affinity.hh"
#if HAVE_SCHED_H
#include <sched.h>
#endif
namespace nix {
static bool didSaveAffinity = false;
static cpu_set_t savedAffinity;
void setAffinityTo(int cpu)
{
#if HAVE_SCHED_SETAFFINITY
if (sched_getaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1) return;
didSaveAffinity = true;
printMsg(lvlDebug, 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)
printMsg(lvlError, format("failed to lock thread to CPU %1%") % cpu);
#endif
}
int lockToCurrentCPU()
{
#if HAVE_SCHED_SETAFFINITY
if (getEnv("NIX_AFFINITY_HACK", "1") == "1") {
int cpu = sched_getcpu();
if (cpu != -1) setAffinityTo(cpu);
return cpu;
}
#endif
return -1;
}
void restoreAffinity()
{
#if HAVE_SCHED_SETAFFINITY
if (!didSaveAffinity) return;
if (sched_setaffinity(0, sizeof(cpu_set_t), &savedAffinity) == -1)
printMsg(lvlError, "failed to restore affinity %1%");
#endif
}
}