FFTView poor performance as time passes #91

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1. alexdmotoc

   added

   bugSomething isn't workingSomething isn't working

   on Jul 15, 2024
2. mahal commented on Aug 3, 2024

   

   mahal

   on Aug 3, 2024

   Last edited by mahal

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   The bug is fully reproducible. Leaving the App open for some more minutes even leads to a crash. I'll have a quick look into the crash to gather more information.
3. mahal commented on Aug 3, 2024

   

   mahal

   on Aug 3, 2024

   Last edited by mahal

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   Findings without looking at the code:

   • View uses 13% CPU on my blue iPhone even when no sound is playing. Partly to AURemoteIO and partly on main thread.
   • View uses roughly 50% CPU when sound is playing: Partly in SwiftUI.AsyncRenderer
   • When sound is playing: Memory footprint constantly increasest at a rate of 100KB per second
   • CPU usage constantly increases, to 100% in a about a minute. On main thread
   • Memory Graph:
     • There's a UICollectionView List with about 1200 Mutable Dictionaries. These dictionaries contain some runtime information (see below)
     • There are more than 3000 CFStrings lingering around, showing a orange icond with a drop. The contain all the same value eyJEQkd [...] Ijp0cnVlfQ==
     • The Mutable Dictionaires are inited by the CFPrefs and by a CGPath (moveto, quadto, lineto, ...)
   • View Hierarchy with clipped content shows a grotesque amount of ZStacks (see attached screenshot)
   • Xcode shows an Optimization Opportunity: "The layer is using dynamic shadows which are expensive to render. If possible try setting shadowPath, or pre-rendering the shadow into an image and putting it under the layer."
   • Pausing and continuing the app with Debugger: Memory clears, CPU usage dropts to 40% and starts increasing again.

   It looks like a memory leak or some silly code that creates elements in a tight loop and garbage collector / reference counter can't act quick enough to free the memory again.

   Starting the app with attached debugger will not lead to a crash, even after running for more than an hour (on CPU 100%).

   Next step: Look into the code to understand where all these dicts come from.

   {
       "ALU instruction count" = 24;
       "Branch instruction count" = 0;
       "Compilation time in milliseconds" = "3.817916";
       "Constant calculation phase present" = 0;
       "Constant calculation temporary register count" = 0;
       "Device atomic instruction count" = 0;
       "Device load instruction count" = 0;
       "Device store instruction count" = 0;
       "FP16 instruction count" = 15;
       "FP32 instruction count" = 8;
       FragmentBufferPrefetch =     (
           promoted
       );
       "INT16 instruction count" = 0;
       "INT32 instruction count" = 0;
       "Instruction count" = 34;
       Remarks = "--- !Analysis\nPass:            prologepilog\nName:            StackSize\nFunction:        agc.main\nArgs:\n  - NumStackBytes:   '0'\n  - String:          ' stack bytes in function'\n...\n--- !Analysis\nPass:            asm-printer\nName:            InstructionMix\nFunction:        agc.main\nArgs:\n  - String:          'BasicBlock: '\n  - BasicBlock:      wrapper_exit\n  - String:          \"\\n\"\n  - String:          ''\n  - String:          ': '\n  - INST_:           '34'\n  - String:          \"\\n\"\n...\n--- !Analysis\nPass:            asm-printer\nName:            InstructionCount\nFunction:        agc.main\nArgs:\n  - NumInstructions: '34'\n  - String:          ' instructions in function'\n...\n";
       "Spilled bytes" = 0;
       "Telemetry Statistics" =     {
       };
       "Temporary register count" = 8;
       "Texture reads instruction count" = 0;
       "Texture writes instruction count" = 0;
       "Thread invariant spilled bytes" = 0;
       "Threadgroup atomic instruction count" = 0;
       "Threadgroup load instruction count" = 0;
       "Threadgroup memory" = 32;
       "Threadgroup store instruction count" = 0;
       "Uniform register count" = 8;
       "Wait instruction count" = 4;
   }
   

   

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4. mahal commented on Aug 3, 2024

   

   mahal

   on Aug 3, 2024

   Last edited by mahal

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   Code analysis:

   • No Strings and dicts are explicitely created. Could it be due to some debugging stuff? will a release build also have the same problems?
   • Fresh FFT results might come too quick
   • .animation of AmplitudeBar and Cap View might interfere with fresh FFT data: the animation is running until the end even when fresh data is already shown
   • .drawingGroup (Metal rendering) is on HStack, it might be better on each bar (because of List View)
   • GeometryReader in a thight loop (ForEach fresh amplitude reading), this is discouraged by Apple. The width and height could be read once (on appear and on change of orientation / layout) and the passed to the other views in @Environment or as a member

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5. alexdmotoc commented on Aug 3, 2024

   

   alexdmotoc

   on Aug 3, 2024

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   @mahal appreciate your insight on this! To me it seems SwiftUI rendering is messing something up, as you showed the huge amount of views rendered one on top of another... I bet that's the key area to look in.

   In the mean time I just replace the rendering with Charts (iOS 16+) and it works perfect

       var body: some View {
           GeometryReader { geometry in
               ZStack {
                   Chart(Array(0 ..< barCount), id: \.self) { index in
                       makeBar(
                           index: index,
                           amplitude: amplitude(at: index),
                           viewHeight: geometry.size.height
                       )
                   }
                   .chartYScale(domain: 0 ... 0.9)
                   .chartXAxis(.hidden)
                   .chartYAxis(.hidden)
               }
           }
           .onAppear {
               fft.maxAmplitude = self.maxAmplitude
               fft.minAmplitude = self.minAmplitude
               callbacks.update = fft.update(buffer:)
               callbacks.start = fft.start
               callbacks.stop = fft.stop
           }
           .background(backgroundColor)
       }
   
       private func makeBar(index: Int, amplitude: Float, viewHeight: CGFloat) -> some ChartContent {
           BarMark(
               x: .value("Frequency", String(index)),
               y: .value("Amplitude", amplitude)
           )
           .foregroundStyle(
               linearGradient.in(CGRect(x: 0, y: 0, width: 0, height: viewHeight))
           )
       }
   
       private func amplitude(at index: Int) -> Float {
           if index < fft.amplitudes.count {
               return fft.amplitudes[index]
           } else {
               return Constants.silence
           }
       }

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