drivers/md/dm-vdo/cpu.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * Copyright 2023 Red Hat
   4  */
   5
   6 #ifndef UDS_CPU_H
   7 #define UDS_CPU_H
   8
   9 #include <linux/cache.h>
  10
  11 /**
  12  * uds_prefetch_address() - Minimize cache-miss latency by attempting to move data into a CPU cache
  13  *                          before it is accessed.
  14  *
  15  * @address: the address to fetch (may be invalid)
  16  * @for_write: must be constant at compile time--false if for reading, true if for writing
  17  */
  18 static inline void uds_prefetch_address(const void *address, bool for_write)
  19 {
  20         /*
  21          * for_write won't be a constant if we are compiled with optimization turned off, in which
  22          * case prefetching really doesn't matter. clang can't figure out that if for_write is a
  23          * constant, it can be passed as the second, mandatorily constant argument to prefetch(),
  24          * at least currently on llvm 12.
  25          */
  26         if (__builtin_constant_p(for_write)) {
  27                 if (for_write)
  28                         __builtin_prefetch(address, true);
  29                 else
  30                         __builtin_prefetch(address, false);
  31         }
  32 }
  33
  34 /**
  35  * uds_prefetch_range() - Minimize cache-miss latency by attempting to move a range of addresses
  36  *                        into a CPU cache before they are accessed.
  37  *
  38  * @start: the starting address to fetch (may be invalid)
  39  * @size: the number of bytes in the address range
  40  * @for_write: must be constant at compile time--false if for reading, true if for writing
  41  */
  42 static inline void uds_prefetch_range(const void *start, unsigned int size,
  43                                       bool for_write)
  44 {
  45         /*
  46          * Count the number of cache lines to fetch, allowing for the address range to span an
  47          * extra cache line boundary due to address alignment.
  48          */
  49         const char *address = (const char *) start;
  50         unsigned int offset = ((uintptr_t) address % L1_CACHE_BYTES);
  51         unsigned int cache_lines = (1 + ((size + offset) / L1_CACHE_BYTES));
  52
  53         while (cache_lines-- > 0) {
  54                 uds_prefetch_address(address, for_write);
  55                 address += L1_CACHE_BYTES;
  56         }
  57 }
  58
  59 #endif /* UDS_CPU_H */