diff --git a/src/libexpr/parallel-eval.cc b/src/libexpr/parallel-eval.cc
index a2955961e063..e0cdab93a7b8 100644
--- a/src/libexpr/parallel-eval.cc
+++ b/src/libexpr/parallel-eval.cc
@@ -134,10 +134,15 @@ std::vector<std::future<void>> Executor::spawn(WorkItems && items)
         for (auto & item : items) {
             std::promise<void> promise;
             futures.push_back(promise.get_future());
-            [[gnu::tls_model("initial-exec")]] static thread_local std::random_device rd;
+            /* Note: this uses a cheap PRNG rather than std::random_device,
+               since the latter costs hundreds of cycles per call (RDRAND or
+               /dev/urandom), which adds up when spawning many work items. The
+               key only needs to spread items of the same priority around the
+               queue, not be cryptographically random. */
+            [[gnu::tls_model("initial-exec")]] static thread_local std::mt19937_64 rng{std::random_device{}()};
             [[gnu::tls_model("initial-exec")]] static thread_local std::uniform_int_distribution<uint64_t> dist(
                 0, 1ULL << 48);
-            auto key = (uint64_t(item.second) << 48) | dist(rd);
+            auto key = (uint64_t(item.second) << 48) | dist(rng);
             state->queue.emplace(key, Item{.promise = std::move(promise), .work = std::move(item.first)});
         }
     }
diff --git a/src/nix/search.cc b/src/nix/search.cc
index d1cebbac67a9..4d1abf24a690 100644
--- a/src/nix/search.cc
+++ b/src/nix/search.cc
@@ -114,6 +114,12 @@ struct CmdSearch : InstallableValueCommand, MixJSON
                             work,
                             std::string_view(state->symbols[attr]).find("Packages") != std::string_view::npos ? 0 : 2,
                             [cursor2, attrPath2, visit]() { visit(*cursor2, attrPath2, false); });
+                        /* Spawn incrementally rather than after the whole
+                           enumeration, so that idle worker threads can start
+                           on the first attributes while we're still
+                           enumerating the rest. */
+                        if (work.size() >= 256)
+                            futures.spawn(std::exchange(work, {}));
                     }
                     futures.spawn(std::move(work));
                 };