(wall, native)_clock: Add GetGPUTick

Allows us to directly calculate the GPU tick without double conversion to and from the host clock tick.

src/common/wall_clock.cpp

@@ -32,6 +32,10 @@ public:
         return GetHostTicksElapsed() * NsToCNTPCTRatio::num / NsToCNTPCTRatio::den;
     }
 
+    u64 GetGPUTick() const override {
+        return GetHostTicksElapsed() * NsToGPUTickRatio::num / NsToGPUTickRatio::den;
+    }
+
     u64 GetHostTicksNow() const override {
         return static_cast<u64>(SteadyClock::Now().time_since_epoch().count());
     }
@@ -52,12 +56,12 @@ std::unique_ptr<WallClock> CreateOptimalClock() {
 #ifdef ARCHITECTURE_x86_64
     const auto& caps = GetCPUCaps();
 
-    if (caps.invariant_tsc && caps.tsc_frequency >= WallClock::CNTFRQ) {
+    if (caps.invariant_tsc && caps.tsc_frequency >= WallClock::GPUTickFreq) {
         return std::make_unique<X64::NativeClock>(caps.tsc_frequency);
     } else {
         // Fallback to StandardWallClock if the hardware TSC
         // - Is not invariant
-        // - Is not more precise than CNTFRQ
+        // - Is not more precise than GPUTickFreq
         return std::make_unique<StandardWallClock>();
     }
 #else

src/common/wall_clock.h

@@ -13,7 +13,8 @@ namespace Common {
 
 class WallClock {
 public:
-    static constexpr u64 CNTFRQ = 19'200'000; // CNTPCT_EL0 Frequency = 19.2 MHz
+    static constexpr u64 CNTFRQ = 19'200'000;       // CNTPCT_EL0 Frequency = 19.2 MHz
+    static constexpr u64 GPUTickFreq = 614'400'000; // GM20B GPU Tick Frequency = 614.4 MHz
 
     virtual ~WallClock() = default;
 
@@ -29,6 +30,9 @@ public:
     /// @returns The guest CNTPCT ticks since the construction of this clock.
     virtual u64 GetCNTPCT() const = 0;
 
+    /// @returns The guest GPU ticks since the construction of this clock.
+    virtual u64 GetGPUTick() const = 0;
+
     /// @returns The raw host timer ticks since an indeterminate epoch.
     virtual u64 GetHostTicksNow() const = 0;
 
@@ -46,6 +50,10 @@ public:
         return us * UsToCNTPCTRatio::num / UsToCNTPCTRatio::den;
     }
 
+    static inline u64 NSToGPUTick(u64 ns) {
+        return ns * NsToGPUTickRatio::num / NsToGPUTickRatio::den;
+    }
+
     static inline u64 CNTPCTToNS(u64 cntpct) {
         return cntpct * NsToCNTPCTRatio::den / NsToCNTPCTRatio::num;
     }
@@ -54,6 +62,14 @@ public:
         return cntpct * UsToCNTPCTRatio::den / UsToCNTPCTRatio::num;
     }
 
+    static inline u64 GPUTickToNS(u64 gpu_tick) {
+        return gpu_tick * NsToGPUTickRatio::den / NsToGPUTickRatio::num;
+    }
+
+    static inline u64 CNTPCTToGPUTick(u64 cntpct) {
+        return cntpct * CNTPCTToGPUTickRatio::num / CNTPCTToGPUTickRatio::den;
+    }
+
 protected:
     using NsRatio = std::nano;
     using UsRatio = std::micro;
@@ -63,6 +79,8 @@ protected:
     using NsToMsRatio = std::ratio_divide<std::nano, std::milli>;
     using NsToCNTPCTRatio = std::ratio<CNTFRQ, std::nano::den>;
     using UsToCNTPCTRatio = std::ratio<CNTFRQ, std::micro::den>;
+    using NsToGPUTickRatio = std::ratio<GPUTickFreq, std::nano::den>;
+    using CNTPCTToGPUTickRatio = std::ratio<GPUTickFreq, CNTFRQ>;
 };
 
 std::unique_ptr<WallClock> CreateOptimalClock();

src/common/x64/native_clock.cpp

@@ -12,7 +12,8 @@ NativeClock::NativeClock(u64 rdtsc_frequency_)
       ns_rdtsc_factor{GetFixedPoint64Factor(NsRatio::den, rdtsc_frequency)},
       us_rdtsc_factor{GetFixedPoint64Factor(UsRatio::den, rdtsc_frequency)},
       ms_rdtsc_factor{GetFixedPoint64Factor(MsRatio::den, rdtsc_frequency)},
-      cntpct_rdtsc_factor{GetFixedPoint64Factor(CNTFRQ, rdtsc_frequency)} {}
+      cntpct_rdtsc_factor{GetFixedPoint64Factor(CNTFRQ, rdtsc_frequency)},
+      gputick_rdtsc_factor{GetFixedPoint64Factor(GPUTickFreq, rdtsc_frequency)} {}
 
 std::chrono::nanoseconds NativeClock::GetTimeNS() const {
     return std::chrono::nanoseconds{MultiplyHigh(GetHostTicksElapsed(), ns_rdtsc_factor)};
@@ -30,6 +31,10 @@ u64 NativeClock::GetCNTPCT() const {
     return MultiplyHigh(GetHostTicksElapsed(), cntpct_rdtsc_factor);
 }
 
+u64 NativeClock::GetGPUTick() const {
+    return MultiplyHigh(GetHostTicksElapsed(), gputick_rdtsc_factor);
+}
+
 u64 NativeClock::GetHostTicksNow() const {
     return FencedRDTSC();
 }

src/common/x64/native_clock.h

@@ -19,6 +19,8 @@ public:
 
     u64 GetCNTPCT() const override;
 
+    u64 GetGPUTick() const override;
+
     u64 GetHostTicksNow() const override;
 
     u64 GetHostTicksElapsed() const override;
@@ -33,6 +35,7 @@ private:
     u64 us_rdtsc_factor;
     u64 ms_rdtsc_factor;
     u64 cntpct_rdtsc_factor;
+    u64 gputick_rdtsc_factor;
 };
 
 } // namespace Common::X64

src/core/core_timing.cpp

@@ -197,6 +197,13 @@ u64 CoreTiming::GetClockTicks() const {
     return ticks;
 }
 
+u64 CoreTiming::GetGPUTicks() const {
+    if (is_multicore) [[likely]] {
+        return clock->GetGPUTick();
+    }
+    return Common::WallClock::CNTPCTToGPUTick(ticks);
+}
+
 std::optional<s64> CoreTiming::Advance() {
     std::scoped_lock lock{advance_lock, basic_lock};
     global_timer = GetGlobalTimeNs().count();

src/core/core_timing.h

@@ -119,6 +119,9 @@ public:
     /// Returns the current CNTPCT tick value.
     u64 GetClockTicks() const;
 
+    /// Returns the current GPU tick value.
+    u64 GetGPUTicks() const;
+
     /// Returns current time in microseconds.
     std::chrono::microseconds GetGlobalTimeUs() const;
 

src/video_core/gpu.cpp

@@ -193,18 +193,13 @@ struct GPU::Impl {
     }
 
     [[nodiscard]] u64 GetTicks() const {
-        // This values were reversed engineered by fincs from NVN
-        // The GPU clock is 614.4 MHz
-        using NsToGPUTickRatio = std::ratio<614'400'000, std::nano::den>;
-        static_assert(NsToGPUTickRatio::num == 384 && NsToGPUTickRatio::den == 625);
-
-        u64 nanoseconds = system.CoreTiming().GetGlobalTimeNs().count();
+        u64 gpu_tick = system.CoreTiming().GetGPUTicks();
 
         if (Settings::values.use_fast_gpu_time.GetValue()) {
-            nanoseconds /= 256;
+            gpu_tick /= 256;
         }
 
-        return nanoseconds * NsToGPUTickRatio::num / NsToGPUTickRatio::den;
+        return gpu_tick;
     }
 
     [[nodiscard]] bool IsAsync() const {