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ui: log guest present cadence statistics behind a debug cvar

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mchughalex 2026-07-22 19:50:53 +01:00
parent 134a1c8f5e
commit 79761cbdd5
1 changed files with 42 additions and 0 deletions
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42
src/ui/presenter.cpp
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@ -13,6 +13,7 @@
#include <atomic>
#include <cctype>
#include <chrono>
#include <cmath>
#include <utility>
#include <rex/assert.h>
@ -45,6 +46,13 @@ REXCVAR_DEFINE_INT32(presenter_strict_guest_output_backpressure_timeout_ms, 100,
.range(0, 1000)
.lifecycle(rex::cvar::Lifecycle::kHotReload);
REXCVAR_DEFINE_BOOL(presenter_present_cadence_log, false, "UI/Presenter",
"Log guest present cadence statistics every 600 swaps: average/max "
"swap-to-swap interval, standard deviation, and frame-to-frame jitter "
"(mean absolute successive difference). Attributes perceived judder to "
"irregular present timing versus low frame rate.")
.lifecycle(rex::cvar::Lifecycle::kHotReload);
REXCVAR_DEFINE_BOOL(present_letterbox, true, "UI/Presenter",
"Enable letterboxing for non-native aspect ratios");
@ -585,6 +593,40 @@ bool Presenter::RefreshGuestOutput(
return false;
}
guest_output_active_last_refresh_ = true;
// Present-cadence telemetry: the interval between guest output refreshes
// is the cadence the host presents at (painting is triggered per
// refresh), which VRR displays turn directly into perceived smoothness.
// jitter = mean absolute successive frame-to-frame difference, the
// judder-relevant metric; sd and max catch slow drift and hitches.
if (REXCVAR_GET(presenter_present_cadence_log)) {
static std::chrono::steady_clock::time_point s_cad_prev{};
static double s_cad_sum = 0, s_cad_sumsq = 0, s_cad_max = 0;
static double s_cad_jitter_sum = 0, s_cad_last = 0;
static uint32_t s_cad_n = 0;
const auto cad_now = std::chrono::steady_clock::now();
if (s_cad_prev.time_since_epoch().count() != 0) {
const double ms =
std::chrono::duration<double, std::milli>(cad_now - s_cad_prev).count();
s_cad_sum += ms;
s_cad_sumsq += ms * ms;
s_cad_max = std::max(s_cad_max, ms);
if (s_cad_n != 0) {
s_cad_jitter_sum += std::abs(ms - s_cad_last);
}
s_cad_last = ms;
if (++s_cad_n >= 600) {
const double avg = s_cad_sum / s_cad_n;
const double var = std::max(0.0, s_cad_sumsq / s_cad_n - avg * avg);
REXLOG_INFO(
"present-cadence: avg={:.2f}ms sd={:.2f} jitter={:.3f} max={:.2f} "
"(600 swaps)",
avg, std::sqrt(var), s_cad_jitter_sum / (s_cad_n - 1), s_cad_max);
s_cad_sum = s_cad_sumsq = s_cad_max = s_cad_jitter_sum = s_cad_last = 0;
s_cad_n = 0;
}
}
s_cad_prev = cad_now;
}
if (GuestFrameStatsEnabled()) {
std::lock_guard<std::mutex> stats_lock(guest_frame_stats_mutex_);
guest_frame_timestamps_[guest_frame_timestamp_next_] = std::chrono::steady_clock::now();