PetscPrefetchBlock#

Prefetches a block of memory

Synopsis#

#include <petscsys.h>
void PetscPrefetchBlock(const anytype *a, size_t n, int rw, int t)

Not Collective

Input Parameters#

a - pointer to first element to fetch (any type but usually PetscInt or PetscScalar)
n - number of elements to fetch
rw - 1 if the memory will be written to, otherwise 0 (ignored by many processors)
t - temporal locality (PETSC_PREFETCH_HINT_{NTA,T0,T1,T2}), see note

Notes#

The last two arguments (rw and t) must be compile-time constants.

Adopting Intel’s x86/x86-64 conventions, there are four levels of temporal locality. Not all architectures offer equivalent locality hints, but the following macros are always defined to their closest analogue.

PETSC_PREFETCH_HINT_NTA - Non-temporal. Prefetches directly to L1, evicts to memory (skips higher level cache unless it was already there when prefetched).
PETSC_PREFETCH_HINT_T0 - Fetch to all levels of cache and evict to the closest level. Use this when the memory will be reused regularly despite necessary eviction from L1.
PETSC_PREFETCH_HINT_T1 - Fetch to level 2 and higher (not L1). On many systems, PETSC_PREFETCH_HINT_T0 and PETSC_PREFETCH_HINT_T1 are equivalent.
PETSC_PREFETCH_HINT_T2 - Fetch to high-level cache only.

This function does nothing on architectures that do not support prefetch and never errors (even if passed an invalid address).

Level#

developer

Location#

include/petscsys.h

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