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EvalState: Don't maintain stats by default

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These counters are extremely expensive in a multi-threaded
program. For instance, disabling them speeds up evaluation of the
NixOS/nix/2.21.2 from 32.6s to 17.8s.
This commit is contained in:
Eelco Dolstra 2025-08-25 20:06:00 +02:00 • committed by Jörg Thalheim
parent 8d257f5510
commit e8f951289f
6 changed files with 94 additions and 20 deletions
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11
src/libexpr/eval.cc
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@ -287,6 +287,7 @@ EvalState::EvalState(
assertGCInitialized();
static_assert(sizeof(Env) <= 16, "environment must be <= 16 bytes");
static_assert(sizeof(Counter) == 64, "counters must be 64 bytes");
/* Construct the Nix expression search path. */
assert(lookupPath.elements.empty());
@ -892,7 +893,7 @@ Value * EvalState::getBool(bool b)
return b ? &Value::vTrue : &Value::vFalse;
}
static std::atomic<uint64_t> nrThunks = 0;
static Counter nrThunks;
static inline void mkThunk(Value & v, Env & env, Expr * expr)
{
@ -2891,11 +2892,11 @@ bool EvalState::fullGC()
#endif
}
bool Counter::enabled = getEnv("NIX_SHOW_STATS").value_or("0") != "0";
void EvalState::maybePrintStats()
{
bool showStats = getEnv("NIX_SHOW_STATS").value_or("0") != "0";
if (showStats) {
if (Counter::enabled) {
// Make the final heap size more deterministic.
#if NIX_USE_BOEHMGC
if (!fullGC()) {
@ -2944,7 +2945,7 @@ void EvalState::printStatistics()
{"elements", nrValuesInEnvs.load()},
{"bytes", bEnvs},
};
topObj["nrExprs"] = Expr::nrExprs;
topObj["nrExprs"] = Expr::nrExprs.load();
topObj["list"] = {
{"elements", nrListElems.load()},
{"bytes", bLists},