60 lines
1.9 KiB
C
60 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Copyright 2023 Red Hat
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*/
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#ifndef UDS_CPU_H
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#define UDS_CPU_H
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#include <linux/cache.h>
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/**
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* uds_prefetch_address() - Minimize cache-miss latency by attempting to move data into a CPU cache
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* before it is accessed.
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*
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* @address: the address to fetch (may be invalid)
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* @for_write: must be constant at compile time--false if for reading, true if for writing
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*/
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static inline void uds_prefetch_address(const void *address, bool for_write)
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{
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/*
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* for_write won't be a constant if we are compiled with optimization turned off, in which
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* case prefetching really doesn't matter. clang can't figure out that if for_write is a
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* constant, it can be passed as the second, mandatorily constant argument to prefetch(),
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* at least currently on llvm 12.
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*/
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if (__builtin_constant_p(for_write)) {
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if (for_write)
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__builtin_prefetch(address, true);
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else
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__builtin_prefetch(address, false);
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}
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}
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/**
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* uds_prefetch_range() - Minimize cache-miss latency by attempting to move a range of addresses
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* into a CPU cache before they are accessed.
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*
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* @start: the starting address to fetch (may be invalid)
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* @size: the number of bytes in the address range
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* @for_write: must be constant at compile time--false if for reading, true if for writing
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*/
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static inline void uds_prefetch_range(const void *start, unsigned int size,
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bool for_write)
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{
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/*
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* Count the number of cache lines to fetch, allowing for the address range to span an
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* extra cache line boundary due to address alignment.
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*/
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const char *address = (const char *) start;
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unsigned int offset = ((uintptr_t) address % L1_CACHE_BYTES);
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unsigned int cache_lines = (1 + ((size + offset) / L1_CACHE_BYTES));
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while (cache_lines-- > 0) {
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uds_prefetch_address(address, for_write);
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address += L1_CACHE_BYTES;
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}
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}
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#endif /* UDS_CPU_H */
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