diff --git a/docs/TCP_COMMANDS.md b/docs/TCP_COMMANDS.md
index 9a686e77..e65796f4 100644
--- a/docs/TCP_COMMANDS.md
+++ b/docs/TCP_COMMANDS.md
@@ -737,6 +737,7 @@ Regenerate with `python tools/gen_tcp_commands.py`; `--check` fails if this bloc
 | `pc_probe_arm` | ✓ |  |  |
 | `pc_probe_clear` | ✓ |  |  |
 | `pc_probe_dump` | ✓ |  |  |
+| `perf` | ✓ |  |  |
 | `pgxp` | ✓ |  | ✓ |
 | `pgxp_miss_ring` | ✓ |  |  |
 | `pgxp_shadow` | ✓ |  |  |
diff --git a/runtime/include/video_telemetry.h b/runtime/include/video_telemetry.h
index 55ae2753..4b9e6cc4 100644
--- a/runtime/include/video_telemetry.h
+++ b/runtime/include/video_telemetry.h
@@ -30,6 +30,18 @@ void psx_video_telemetry_present(int result);
  * Completion/error counters remain available in that case. */
 void psx_video_telemetry_snapshot(PsxVideoTelemetry *out);
 
+typedef struct PsxPresentCadence {
+    int valid;
+    uint32_t count, mean_us, p50_us, p95_us, p99_us, max_us, hitches;
+    double span_ms, fps;
+} PsxPresentCadence;
+/* Host API completion intervals, shared by all backends; no monitor-display
+ * guarantee. Bounded passive snapshot. reset is consumed by the presenter. */
+void psx_video_telemetry_cadence(int window_ms, int reset, PsxPresentCadence *out);
+int psx_video_telemetry_cadence_json(int window_ms, int reset, char *out, int capacity);
+/* Explicit monotonic host microseconds for adapters and deterministic tests. */
+void psx_video_telemetry_present_at(int result, uint64_t now_us);
+
 /* Emulation-owner settings after runtime mod overrides, sampled every VBlank.
  * Actual allocated scale/dimensions come from the separate backend snapshot. */
 typedef struct PsxVideoConfigTelemetry {
diff --git a/runtime/src/debug_server.c b/runtime/src/debug_server.c
index 3dfc9c89..3055bb6c 100644
--- a/runtime/src/debug_server.c
+++ b/runtime/src/debug_server.c
@@ -9447,6 +9447,15 @@ static void handle_ws_aspect(int id, const char *json)
 }
 
 extern int psx_debug_display_aspect(int num, int den, int adaptive);
+/* perf: host API completion cadence across the active presentation backend. */
+extern int psx_video_telemetry_cadence_json(int window_ms, int reset, char *out, int cap);
+static void handle_perf(int id, const char *json) {
+    char buf[512];
+    psx_video_telemetry_cadence_json(json_get_int(json, "window_ms", 0), json_get_int(json, "reset", 0),
+                           buf, sizeof buf);
+    send_fmt("{\"id\":%d,\"ok\":true,%s}", id, buf);
+}
+
 static void handle_display_aspect(int id, const char *json) {
     int num=json_get_int(json,"num",-1), den=json_get_int(json,"den",-1);
     int adaptive=json_get_int(json,"adaptive",0);
@@ -16370,6 +16379,7 @@ static const CmdEntry s_commands[] = {
     { "kernel_bless",      handle_kernel_bless },
     { "ws_aspect",         handle_ws_aspect },
     { "display_aspect",    handle_display_aspect },
+    { "perf",              handle_perf },
     { "window_size",       handle_window_size },
     { "ws_nw",             handle_ws_nw },
     { "debug_key",         handle_debug_key },
diff --git a/runtime/src/main.cpp b/runtime/src/main.cpp
index cb5e61c7..8b00f22d 100644
--- a/runtime/src/main.cpp
+++ b/runtime/src/main.cpp
@@ -9263,6 +9263,15 @@ static NetplayVblankEpilogue sdl_vblank_present_body(void) {
                     snprintf(title, sizeof(title), "%s  [Game %.0f fps %.2fx]",
                              s_fps_base_title.c_str(), fps, speed);
                 }
+                {
+                    PsxPresentCadence cadence{};
+                    psx_video_telemetry_cadence(1000, 0, &cadence);
+                    const double sfps = cadence.fps;
+                    const unsigned hitch = cadence.hitches, worst = cadence.max_us / 1000;
+                    size_t l = strlen(title);
+                    snprintf(title + l, sizeof(title) - l, " [Present %.1f fps, %u hitch, max %u ms]",
+                             sfps, hitch, worst);
+                }
                 SDL_SetWindowTitle(sdl_window, title);
             }
             if (!g_headless) {
diff --git a/runtime/src/video_telemetry.cpp b/runtime/src/video_telemetry.cpp
index c430194d..4f97b468 100644
--- a/runtime/src/video_telemetry.cpp
+++ b/runtime/src/video_telemetry.cpp
@@ -1,11 +1,23 @@
 #include "video_telemetry.h"
 #include <atomic>
+#include <algorithm>
+#include <chrono>
+#include <cstdio>
+#include <limits>
 
 namespace {
 std::atomic<uint64_t> presents{0}, errors{0};
 std::atomic<int> status_available{0};
 std::atomic<unsigned> generation{0};
 std::atomic<int> fields[8]{};
+constexpr unsigned cadence_capacity = 4096;
+std::atomic<uint32_t> intervals[cadence_capacity]{};
+std::atomic<uint64_t> cadence_version{0}, cadence_count{0};
+std::atomic<bool> cadence_reset{false};
+// Only the current present owner touches these. Readers request reset rather
+// than changing the producer's cursor or timestamp.
+uint64_t last_present_us;
+bool have_last_present;
 }
 
 extern "C" void psx_video_telemetry_compose(int renderer, int scale, int sw, int sh,
@@ -20,8 +32,75 @@ extern "C" void psx_video_telemetry_compose(int renderer, int scale, int sw, int
 }
 
 extern "C" void psx_video_telemetry_present(int result) {
+    const auto now = std::chrono::steady_clock::now().time_since_epoch();
+    psx_video_telemetry_present_at(result,
+        std::chrono::duration_cast<std::chrono::microseconds>(now).count());
+}
+
+extern "C" void psx_video_telemetry_present_at(int result, uint64_t now_us) {
     status_available.store(result >= 0, std::memory_order_relaxed);
     (result != 0 ? presents : errors).fetch_add(1, std::memory_order_relaxed);
+    if (result == 0) return;
+    cadence_version.fetch_add(1);
+    if (cadence_reset.exchange(false)) {
+        cadence_count.store(0);
+        have_last_present = false;
+    }
+    if (have_last_present && now_us > last_present_us) {
+        const uint64_t count = cadence_count.load();
+        const auto delta = std::min<uint64_t>(now_us - last_present_us, UINT32_MAX);
+        intervals[count % cadence_capacity].store(static_cast<uint32_t>(delta));
+        cadence_count.store(count + 1);
+    }
+    last_present_us = now_us;
+    have_last_present = true;
+    cadence_version.fetch_add(1);
+}
+
+extern "C" void psx_video_telemetry_cadence(int window_ms, int reset, PsxPresentCadence *out) {
+    if (!out) return;
+    *out = {};
+    uint32_t values[cadence_capacity]; // each reader owns its sorting storage
+    uint64_t sum = 0;
+    for (unsigned attempt = 0; attempt < 3; ++attempt) {
+        out->count = 0; sum = 0;
+        const uint64_t before = cadence_version.load();
+        if (before & 1u) continue;
+        if (cadence_reset.load()) { out->valid = 1; break; }
+        const uint64_t count = cadence_count.load();
+        const unsigned n = static_cast<unsigned>(std::min<uint64_t>(count, cadence_capacity));
+        for (unsigned i = 0; i < n; ++i) {
+            const uint32_t value = intervals[(count - 1 - i) % cadence_capacity].load();
+            if (window_ms > 0 && sum + value > static_cast<uint64_t>(window_ms) * 1000) break;
+            sum += value; values[out->count++] = value;
+        }
+        if (before == cadence_version.load()) { out->valid = 1; break; }
+    }
+    if (reset) cadence_reset.store(true);
+    if (!out->valid) { *out = {}; return; }
+    if (!out->count) return;
+    std::sort(values, values + out->count);
+    const auto k = out->count;
+    out->mean_us = static_cast<uint32_t>(sum / k);
+    out->p50_us = values[k / 2];
+    out->p95_us = values[(k - 1) * 95 / 100];
+    out->p99_us = values[(k - 1) * 99 / 100];
+    out->max_us = values[k - 1];
+    for (unsigned i = 0; i < k; ++i)
+        if (static_cast<uint64_t>(values[i]) * 2 > static_cast<uint64_t>(out->p50_us) * 3)
+            ++out->hitches;
+    out->span_ms = sum / 1000.0;
+    out->fps = sum ? k * 1e6 / static_cast<double>(sum) : 0;
+}
+
+extern "C" int psx_video_telemetry_cadence_json(int window_ms, int reset, char *out, int capacity) {
+    PsxPresentCadence r{};
+    psx_video_telemetry_cadence(window_ms, reset, &r);
+    return std::snprintf(out, capacity,
+        "\"valid\":%s,\"measurement\":\"host_api_completion\",\"swaps\":%u,\"span_ms\":%.1f,"
+        "\"fps\":%.2f,\"mean_us\":%u,\"p50_us\":%u,\"p95_us\":%u,\"p99_us\":%u,\"max_us\":%u,\"hitches\":%u",
+        r.valid ? "true" : "false", r.count, r.span_ms, r.fps, r.mean_us,
+        r.p50_us, r.p95_us, r.p99_us, r.max_us, r.hitches);
 }
 
 extern "C" void psx_video_telemetry_snapshot(PsxVideoTelemetry *out) {
diff --git a/runtime/tests/test_video_telemetry.cpp b/runtime/tests/test_video_telemetry.cpp
index f89c5013..0abfb90a 100644
--- a/runtime/tests/test_video_telemetry.cpp
+++ b/runtime/tests/test_video_telemetry.cpp
@@ -52,6 +52,42 @@ int main() {
     CHECK(sample.valid && sample.internal_scale == 10000 && sample.presents == 10002);
     CHECK(sample.present_status_available);
     CHECK(sample.present_errors == 1);
+    PsxPresentCadence cadence{};
+    psx_video_telemetry_cadence(0,1,&cadence);
+    psx_video_telemetry_present_at(1,1000);
+    psx_video_telemetry_present_at(1,11000);
+    psx_video_telemetry_present_at(-1,21000);
+    psx_video_telemetry_present_at(1,51000);
+    psx_video_telemetry_cadence(0,0,&cadence);
+    CHECK(cadence.valid && cadence.count==3 && cadence.mean_us==16666);
+    CHECK(cadence.p50_us==10000 && cadence.max_us==30000 && cadence.hitches==1);
+    psx_video_telemetry_cadence(35,0,&cadence);
+    CHECK(cadence.valid && cadence.count==1 && cadence.max_us==30000);
+    psx_video_telemetry_cadence(0,1,&cadence);
+    psx_video_telemetry_cadence(0,0,&cadence);
+    CHECK(cadence.valid && !cadence.count);
+    psx_video_telemetry_present_at(1,100000);
+    psx_video_telemetry_cadence(0,0,&cadence);
+    CHECK(cadence.valid && !cadence.count); // producer reset re-anchors timing
+    std::atomic<bool> cadence_done{false};
+    std::atomic<bool> cadence_consistent{true};
+    std::thread presenter([&] {
+        for(uint64_t i=1;i<=20000;++i) psx_video_telemetry_present_at(1,100000+i*10000);
+        cadence_done=true;
+    });
+    auto reader=[&](bool resets) {
+        unsigned reads=0;
+        do {
+            PsxPresentCadence c{};
+            psx_video_telemetry_cadence(0,resets && (++reads%17==0),&c);
+            if(c.valid && c.count && (c.mean_us!=10000 || c.max_us!=10000 || c.hitches!=0))
+                cadence_consistent=false;
+        }while(!cadence_done.load());
+    };
+    std::thread other_reader([&]{reader(true);});
+    reader(false);
+    presenter.join();other_reader.join();
+    CHECK(cadence_consistent.load());
     psx_video_telemetry_snapshot(nullptr);
     return 0;
 }