Describe numpy/MKL issues as comment in dpnp_eig_c (#1006)

Co-authored-by: Alexander-Makaryev <[email protected]>

Author: densmirn

dpnp/backend/kernels/dpnp_krnl_common.cpp

@@ -401,6 +401,15 @@ void dpnp_eig_c(const void* array_in, void* result1, void* result2, size_t size)
     const std::int64_t scratchpad_size = mkl_lapack::syevd_scratchpad_size<double>(
         DPNP_QUEUE, oneapi::mkl::job::vec, oneapi::mkl::uplo::upper, size, lda);
 
+    // https://github.com/IntelPython/dpnp/issues/1005
+    // Test tests/test_linalg.py::test_eig_arange raises 2 issues in dpnp_eig_c on CPU
+    // 1. Call of mkl_lapack::syevd_scratchpad_size<double> returns wrong value that causes out of memory issue.
+    // 2. Call of the function oneapi::mkl::lapack::syevd causes segfault.
+    // Example of the command to reproduce the issues:
+    // SYCL_DEVICE_FILTER=cpu pytest tests/test_linalg.py::test_eig_arange[2-float64]
+    // High-level reason of the issues is numpy is imported before dpnp in third party tests.
+    // Low-level reason of the issues could be related to MKL runtime library loaded during numpy import.
+
     double* scratchpad = reinterpret_cast<double*>(dpnp_memory_alloc_c(scratchpad_size * sizeof(double)));
 
     event = mkl_lapack::syevd(DPNP_QUEUE,               // queue