I'm willing to believe that, but who would use a single core for an embarrassingly parallel problem such as image convolution? I'd expect it to use all 8 cores,

I'm willing to believe that, but who would use a single core for an embarrassingly parallel problem such as image convolution? I'd expect it to use all 8 cores, but AFAIK, Wasm really only uses one. Probably that's the biggest performance factor then.