kermac 0.1.1

Pytorch routines for (Ker)nel (Mac)hines

KERMAC

Kermac is a collection of fused CUDA kernels meant for fast and memory efficient computation for kernel methods. Kermac makes heavy use of JIT (Just-in-time) compilation to generate custom CUDA kernels on demand. These compiled kernels are stored in a cache database so the JIT costs are only incurred once. Using debug=True in most kermac routines will print information related to the compilation and caching of these JIT CUDA kernels.

Kermac supports only Nvidia cards with capability of sm_80 or higher. This includes:

• Server cards like A10, A100, H100, B100
• Consumer cards like RTX 30xx, RTX 40xx, RTX 50xx

Kermac relies on cuda-core for JIT compilation which is supported for cuda toolkits 11.8 and 12.x. Because of cuda-core and nvmath packages no C++ compilation or wheel system is needed to install this library.

Installation

CUDA 12

pip install "kermac[cu12] @ git+https://github.com/Kernel-Machines/kermac"

CUDA 11

pip install "kermac[cu11] @ git+https://github.com/Kernel-Machines/kermac"

Linalg

linalg functionality depends on nvmath-python. This isn't a required dependency. To run linalg routines please do:

pip install nvmath-python[cu12]

or

pip install nvmath-python[cu11]

Examples

From a fresh environment you can do:

cdist.py

wget https://raw.githubusercontent.com/Kernel-Machines/kermac/refs/heads/master/examples/cdist.py
python cdist.py -d -p 1.0

cdist_grad.py

wget https://raw.githubusercontent.com/Kernel-Machines/kermac/refs/heads/master/examples/cdist_grad.py
python cdist_grad.py -d

build_a_kernel.py

Running build_a_kernel.py will batch compile quite a few different kernels on first run. Expect around 20 seconds of JIT compiling.

wget https://raw.githubusercontent.com/Kernel-Machines/kermac/refs/heads/master/examples/build_a_kernel.py
python build_a_kernel.py -d

linalg.py

wget https://raw.githubusercontent.com/Kernel-Machines/kermac/refs/heads/master/examples/linalg.py
python linalg.py

Function: linalg.solve_cholesky

Solves a symmetric system of equations like torch.linalg.cholesky. Wraps xpotrf and xpotrs from nvmath.bindings.cusolverDn. This implementation is special because it doesn't synchronize with the cpu on a failed cholesky factor. Additionally this routine can write the factorization in-place to the input matrix. In some cases this avoids a full 2x increase in memory usage. It launches a separate cuda-stream for each of the batches passed in. It does require a bit of workspace memory allocation for each stream. It synchronizes the cuda-streams against the current stream at the end of the routine.

Function: linalg.solve_lu

Solves a symmetric system of equations like torch.linalg.solve. Wraps xgetrf and xgetrs from nvmath.bindings.cusolverDn. This implementation is special because it doesn't synchronize with the cpu on a failed LU decomposition. Additionally this routine can write the factorization in-place to the input matrix. In some cases this avoids a full 2x increase in memory usage. It launches a separate cuda-stream for each of the batches passed in. It does require a bit of workspace memory allocation for each stream. It synchronizes the cuda-streams against the current stream at the end of the routine.

Function: linalg.eigh

Computes eigenvalues and eigenvectors of a symmetric matrix like torch.linalg.eigh Wraps xsyevd from nvmath.bindings.cusolverDn. This implementation is special because it doesn't synchronize with the cpu on a failed eigenvalue decomposition. Additionally this routine can write the eigenvector decomposition in-place to the input matrix. In some cases this avoids a full 2x increase in memory usage. It launches a separate cuda-stream for each of the batches passed in. It does require a bit of workspace memory allocation for each stream. It synchronizes the cuda-streams against the current stream at the end of the routine.

Function: cdist

An implementation of torch.cdist. Computes fractional norms. Supports batches and broadcasting. Aside from the out tensor in the out=None case does not allocate.

Computes:

$out_{n,m} = \left( \sum_{k=1}^{K} |b_{k,n} - a_{k,m}|^p \right)^{\frac{1}{p}}$

If instead skip_epilogue is set it computes:

$out_{n,m} = \sum_{k=1}^{K} |b_{k,n} - a_{k,m}|^p$

Or expressed in c-style it efficiently computes:

// a[K,M], b[K,N], out[N,M]
for (int m = 0; m < M; m++) {
    for (int n = 0; n < N; n++) {
        for (int k = 0; k < K; k++) {
            out[n,m] += pow(abs(b[k,n] - a[k,m]), p);
        }
        if (!skip_epilogue) {
            out[n,m] = pow(out[n,m], 1.0/p);
        }
    }
}

It has special code paths for $p=1.0$ and $p=2.0$ to avoid fractional power instructions.

kermac.cdist vs torch.cdist

with problem size $[M,N,K]$ = $[30000,30000,1024]$

GPU / p-norm	Speed-up (×)	kermac.cdist (ms)	torch.cdist (ms)
GH200 · p = 1.0	29.1×	82	2,389
GH200 · p = 1.3	9.6×	453	4,360
GH200 · p = 2.0	5.2×	79	406
H100-PCIe · p = 1.0	27.0×	108	2,907
H100-PCIe · p = 1.3	9.4×	592	5,591
H100-PCIe · p = 2.0	3.3×	104	346
A100 · p = 1.0	15.4×	251	3,878
A100 · p = 1.3	9.4×	873	8,230
A100 · p = 2.0	0.9×	325	301
RTX 4090 · p = 1.0	52.6×	76	4,021
RTX 4090 · p = 1.3	11.8×	350	4,141
RTX 4090 · p = 2.0	3.4×	77	262

Function: run_kernel

This is a more customizable version of kermac.cdist, kermac.cdist is written on top of this. run_kernel allows a descriptor as one of it's arguments that can create fully fused kernel functions. You can specify the inner-norm type (abs(x), x*x, or pow(x,p)), the outer-norm type (x, sqrt(x), or pow(x,1/p)) and finally a laplace or gaussian epilogue. On first run a fully fused kernel will be JIT compiled and cached for future use. This function also allows broadcasting and batching of it's input tensors. See build_a_kernel.py for various examples of usage. It also allows batching and broadcasting of it's hyperparameters such as p, bandwidth, and regularization. See broadcast_kernel.py for examples of batching and broadcasting hyperparameters

Function: cdist_grad

Computes the gradient of cdist in the style like:

$out_{o,n,m} = \sum_{k=1}^{K} c_{o,k}a_{k,m}\mathrm{sgn}\left(d_{n,m}-b_{n,k}\right)\left|d_{n,m}-b_{n,k}\right|^{p-1}$

Or expressed in c-style it efficiently computes:

// a[K,M], b[N,K], c[O,K], d[N,M], out[O,N,M]
for (int m = 0; m < M; m++) {
    for (int n = 0; n < N; n++) {
        for (int o = 0; o < O; o++) {
            for (int k = 0; k < K; k++) {
                float diff = d[n,m] - b[n,k];
                out[o,n,m] += c[o,k] * a[k,m] * signum(diff) * pow(abs(diff), p - 1.0));
            }
        }
    }
}

Aside from the out tensor in the out=None case DOES NOT ALLOCATE It has special code paths for $p=1.0$ and $p=2.0$ to avoid fractional power instructions.

It's supposed to be used like:

• $a_{k,m}$ is kernel_matrix
• $b_{n,k}$ is data_x
• $c_{o,k}$ is coefficients
• $d_{n,m}$ is data_z
• $out_{o,n,k}$ is gradient

Tensors must satisfy

# Given tensors a,b,c,d,out and sizes M,N,O,K
# K is the contracted mode
assert a.shape == torch.Size([K,M])
assert b.shape == torch.Size([N,K])
assert c.shape == torch.Size([O,K])
assert d.shape == torch.Size([N,M])
assert out.shape == torch.Size([O,N,M])

assert a.stride(1) == 1
assert b.stride(1) == 1
assert c.stride(1) == 1
assert d.stride(1) == 1
assert out.stride(1) == 1

out = kermac.cdist_grad(a,b,c,d,out=out) # OK

Views are OK