# Benchmarks

## vtebench

All benchmarks are done using [vtebench](https://github.com/alacritty/vtebench):

```sh
vtebench -h $(tput lines) -w $(tput cols) -b 104857600 alt-screen-random-write > ~/alt-random
vtebench -c -h $(tput lines) -w $(tput cols) -b 104857600 alt-screen-random-write > ~/alt-random-colors
vtebench -h $(tput lines) -w $(tput cols) -b 10485760 scrolling > ~/scrolling
vtebench -h $(tput lines) -w $(tput cols) -b 104857600 scrolling --fill-lines > ~/scrolling-filled-lines
vtebench -h $(tput lines) -w $(tput cols) -b 10485760 unicode-random-write > ~/unicode-random
```

They were "executed" using [benchmark.py](../scripts/benchmark.py),
which will load each file into memory, and then print it to the
terminal. This is done **20** times for each test. Then it calculates
the _mean_ and _standard deviation_ for each test.


## 2020-07-25

### System

CPU: i9-9900

RAM: 64GB

Graphics: Radeon RX 5500XT


### Terminal configuration

Geometry: 2040x1884

Font: Fantasque Sans Mono 10.00pt/23px

Scrollback: 10000 lines


### Results

| Benchmark              | Foot (GCC+PGO) 1.4.2.r14 |      Alacritty 0.4.3 |     URxvt 9.22 |      XTerm 358 |
|------------------------|-------------------------:|---------------------:|---------------:|---------------:|
| alt-random             |            0.423s ±0.014 |   0.904s ±0.006      |  1.111s ±0.003 | 12.851s ±0.087 |
| alt-random-colors      |            0.382s ±0.005 |   0.935s ±0.005      |  1.146s ±0.007 | 11.816s ±0.088 |
| scrolling              |            1.380s ±0.048 |   1.011s ±0.012      |  1.021s ±0.016 | 38.483s ±0.122 |
| scrolling-filled-lines |            0.826s ±0.020 |   1.307s ±0.008      |  1.213s ±0.015 |  6.725s ±0.016 |
| unicode-random         |            0.243s ±0.006 |   0.091s ±0.003 [^1] | 24.507s ±3.264 | 26.127s ±3.891 |



## 2020-07-25

### System

CPU: i5-8250U

RAM: 8GB

Graphics: Intel UHD Graphics 620


### Terminal configuration

Geometry: 945x1020

Font: Dina:pixelsize=12

Scrollback=10000 lines


### Results

| Benchmark              | Foot (GCC+PGO) 1.5.0.r27 |     Alacritty 0.5.0 |       URxvt 9.22 |      St 0.8.4 |       XTerm 360 |
|------------------------|-------------------------:|--------------------:|-----------------:|--------------:|----------------:|
| alt-random             |            0.741s ±0.067 |  1.472s ±0.126      |    1.717s ±0.141 | 1.910s ±0.030 |  37.832s ±0.193 |
| alt-random-colors      |            0.735s ±0.050 |  1.510s ±0.084      |    1.936s ±0.121 | 2.114s ±0.116 |  33.759s ±0.344 |
| scrolling              |            1.687s ±0.044 |  1.440s ±0.128      |    1.485s ±0.032 | 3.485s ±0.142 | 134.590s ±0.602 |
| scrolling-filled-lines |            1.331s ±0.041 |  2.072s ±0.073      |    2.031s ±0.087 | 2.658s ±0.084 |  20.508s ±0.063 |
| unicode-random         |            0.303s ±0.010 |  0.155s ±0.006 [^1] | 130.967s ±28.161 |       crashed | 170.444s ±7.798 |

[^1]: [Alacritty and "unicode-random"](#alacritty-and-unicode-random)


# Alacritty and "unicode-random"

Alacritty is actually **really** slow at rendering this (whether it is
fallback fonts in general, emojis, or something else, I don't know).

I believe the reason it finishes the benchmark so quickly is because
it reads from the PTY in a separate thread, into a larger receive
buffer which is then consumed by the main thread. This allows the
client program to write its output much faster since it is no longer
stalling on a blocked PTY.

This means Alacritty only needs to render a couple of frames since it
can reach the final VT state almost immediately.

On the other hand, `cat`:ing the `unicode-random` test file in an
endless loop, or just manually scrolling up after the benchmark is
done is **slow**, which besides being felt (input lag), can be seen by
setting `debug.render_timer = true` in `alacritty.yml`.