Millis() runs slow with t3.6 running 16ch parallel out example

[ryanelm]

The code below outputs the FPS every second, however on a teensy 3.6 running at 180MHZ it takes ~4 seconds. tested on several boards. Also tried elapsedMillis type but it is also slow.

`#include <FastLED.h>

#define NUM_LEDS_PER_STRIP 1024
// Note: this can be 12 if you're using a teensy 3 and don't mind soldering the pads on the back
#define NUM_STRIPS 16

CRGB leds[NUM_STRIPS * NUM_LEDS_PER_STRIP];

// Pin layouts on the teensy 3/3.1:
// WS2811_PORTD: 2,14,7,8,6,20,21,5
// WS2811_PORTC: 15,22,23,9,10,13,11,12,28,27,29,30 (these last 4 are pads on the bottom of the teensy)
// WS2811_PORTDC: 2,14,7,8,6,20,21,5,15,22,23,9,10,13,11,12 - 16 way parallel
//
// Pin layouts on the due
// WS2811_PORTA: 69,68,61,60,59,100,58,31 (note: pin 100 only available on the digix)
// WS2811_PORTB: 90,91,92,93,94,95,96,97 (note: only available on the digix)
// WS2811_PORTD: 25,26,27,28,14,15,29,11
//

// IBCC<WS2811, 1, 16> outputs;

void setup() {
//delay(5000);
Serial.begin(57600);
Serial.println("Starting...");
// LEDS.addLeds<WS2811_PORTA,NUM_STRIPS>(leds, NUM_LEDS_PER_STRIP);
// LEDS.addLeds<WS2811_PORTB,NUM_STRIPS>(leds, NUM_LEDS_PER_STRIP);
// LEDS.addLeds<WS2811_PORTD,NUM_STRIPS>(leds, NUM_LEDS_PER_STRIP).setCorrection(TypicalLEDStrip);
LEDS.addLeds<WS2811_PORTDC, NUM_STRIPS>(leds, NUM_LEDS_PER_STRIP);

// Teensy 4 parallel output example
// LEDS.addLeds<NUM_STRIPS, WS2811, 1>(leds,NUM_LEDS_PER_STRIP);
}

int debugTime = 0;
int fps = 0;
void loop()
{
static int t = millis();
int dt = millis() - t;
t += dt;
debugTime += dt;

if (debugTime > 1000)
{
Serial.println(fps);
Serial.println(debugTime);
debugTime -= 1000;
fps = 0;
}
static uint8_t hue = 0;
static bool ind = true;
for (int i = 0; i < NUM_STRIPS; i++)
{
for (int j = 0; j < NUM_LEDS_PER_STRIP; j++)
{
leds[(i * NUM_LEDS_PER_STRIP) + j] = CHSV((32 * i) + hue + j, 192, 255);
}
}

// Set the first n leds on each strip to show which strip it is
for (int i = 0; i < NUM_STRIPS; i++) {
for (int j = 0; j <= i; j++) {
//leds[(i*NUM_LEDS_PER_STRIP) + j] = ind ? CRGB::Red : CRGB::Green;
}
}

hue++;
ind = !ind;
fps++;
LEDS.show();
}`