High CPU usage

[CardealRusso]

What causes the high CPU usage?

[akkartik]

It's a good question; I see it now. My CPU is pegged at close to 100% (of one core).

Neither fenster nor microUI with SDL are this inefficient.

Even if I drop down from 60fps to 10fps, it still quickly ramps up to 30% CPU core.

I did a quick profile with gprof, and it looks like this:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  Ts/call  Ts/call  name    
 27.58      1.93     1.93                             mu_color
 21.87      3.46     1.53                             blend_pixel
 16.65      4.63     1.17                             r_color
 10.00      5.33     0.70                             flush

Looks like it's because of our extremely naive purely-CPU shading. We're basically recomputing the color of each pixel even when drawing rects with a constant color.

One confound here is that we sometimes need to blend the white from the font within the rect. But perhaps we can get by with a 2-color cache.

Anyways, I've turned on compiler optimizations (-O3) and disabled assertions (-DNDEBUG) and it seems to be running at 30-40% CPU core. So that's something.

[tekknolagi]

There's another project that does caching using microui. I'll see if I can find it later and distill the core of it into this as an optional addon

On October 3, 2024 11:07:53 AM EDT, Kartik Agaram @.***> wrote:

It's a good question; I see it now. My CPU is pegged at close to 100% (of one core).

Neither fenster nor microUI with SDL are this inefficient.

Even if I drop down from 60fps to 10fps, it still quickly ramps up to 30% CPU core.

I did a quick profile with gprof, and it looks like this:

Each sample counts as 0.01 seconds.
 %   cumulative   self              self     total           
time   seconds   seconds    calls  Ts/call  Ts/call  name    
27.58      1.93     1.93                             mu_color
21.87      3.46     1.53                             blend_pixel
16.65      4.63     1.17                             r_color
10.00      5.33     0.70                             flush

Looks like it's because of our extremely naive purely-CPU shading. We're basically recomputing the color of each pixel even when drawing rects with a constant color.

One confound here is that we sometimes need to blend the white from the font within the rect. But perhaps we can get by with a cache.

Anyways, I've turned on compiler optimizations (-O3) and disabled assertions (-DNDEBUG) and it seems to be running at 30-40% CPU core. So that's something.

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[CardealRusso]

-flto cuts cpu usage by almost half But it's still not practical, as usage should remain at 0~1%.

Pixels are unnecessarily updated every frame.