Hardware problem? iphone12 consumes more time on VTCompressionSessionEncodeFrame and AVAssetWriter than iphoneXs

Question

This question is similar with [https://developer.apple.com/forums/thread/127613]

In my demo, the average execution time of VTCompressionSessionEncodeFrame in iphone12 is 10ms while iphoneXs only costs 6ms. If I decrease the frequency of calling that function, the execution time also decreases but the total time(delay+execution time) stays same about 11ms on iphone12 and 7ms on iphoneXs. I try various configuration of VTCompressionSession, but the result (iphone12 > iphoneXs) never change！ Here is the configuration of VTCompressionSession

bool VideoToolboxEncoder::InitCompressionSession() {
  CFMutableDictionaryRef sourceImageBufferAttributes = CFDictionaryCreateMutable(kCFAllocatorDefault, 0, NULL, NULL);
  CFDictionarySetValue(sourceImageBufferAttributes, kCVPixelBufferOpenGLESCompatibilityKey, kCFBooleanTrue);
  CFDictionaryRef io_surface_value = CFDictionaryCreate(kCFAllocatorDefault, NULL, NULL, 0, NULL, NULL);
  CFDictionarySetValue(sourceImageBufferAttributes, kCVPixelBufferIOSurfacePropertiesKey, io_surface_value);
  OSType target_pixelformat = kCVPixelFormatType_420YpCbCr8Planar;
  dict_set_i32(sourceImageBufferAttributes,
                 kCVPixelBufferPixelFormatTypeKey, target_pixelformat);
  dict_set_i32(sourceImageBufferAttributes,
                 kCVPixelBufferBytesPerRowAlignmentKey, 16);
  CFDictionarySetValue(sourceImageBufferAttributes, kCVPixelBufferWidthKey, CFNumberCreate(NULL, kCFNumberIntType, &codec_settings.width));
  CFDictionarySetValue(sourceImageBufferAttributes, kCVPixelBufferHeightKey, CFNumberCreate(NULL, kCFNumberIntType, &codec_settings.height));
  OSStatus status = VTCompressionSessionCreate(NULL,
                                      codec_settings.width,
                                      codec_settings.height,
                                      kCMVideoCodecType_HEVC,
                                      NULL,
                                      sourceImageBufferAttributes,
                                      NULL,
                                      encodeComplete,
                                      this,
                                      &compression_session_);
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_RealTime, kCFBooleanTrue);
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_AllowFrameReordering, kCFBooleanFalse);
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_ExpectedFrameRate, (__bridge CFTypeRef)@(29.97));
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_MaxKeyFrameInterval,
                                (__bridge CFTypeRef)@(codec_settings.gop_size));
  CFStringRef profileRef;
  profileRef = kVTProfileLevel_HEVC_Main_AutoLevel;
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_ProfileLevel, profileRef);
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_AllowOpenGOP, kCFBooleanFalse);
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_AverageBitRate, (__bridge CFTypeRef)@(codec_settings.bitrate));
  status = VTSessionSetProperty(compression_session_, kVTCompressionPropertyKey_DataRateLimits, (__bridge CFTypeRef)@[@20000000, @2]);
  VTCompressionSessionPrepareToEncodeFrames(compression_session_);
  return 0;
}

I also tryed to export video with AVAssetWriter and I got the same result.

It's unexpected that videotoolbox performance decreases on newer iphones. I want to figure out this problem is due to my incorrect configuration or hardware of iphone. Has anyone encountered the same problem？If someone could help with this issue would be really grateful!