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-rw-r--r--drivers/md/dm-vdo/cpu.h59
1 files changed, 59 insertions, 0 deletions
diff --git a/drivers/md/dm-vdo/cpu.h b/drivers/md/dm-vdo/cpu.h
new file mode 100644
index 0000000000..d6a2615ba6
--- /dev/null
+++ b/drivers/md/dm-vdo/cpu.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef UDS_CPU_H
+#define UDS_CPU_H
+
+#include <linux/cache.h>
+
+/**
+ * uds_prefetch_address() - Minimize cache-miss latency by attempting to move data into a CPU cache
+ * before it is accessed.
+ *
+ * @address: the address to fetch (may be invalid)
+ * @for_write: must be constant at compile time--false if for reading, true if for writing
+ */
+static inline void uds_prefetch_address(const void *address, bool for_write)
+{
+ /*
+ * for_write won't be a constant if we are compiled with optimization turned off, in which
+ * case prefetching really doesn't matter. clang can't figure out that if for_write is a
+ * constant, it can be passed as the second, mandatorily constant argument to prefetch(),
+ * at least currently on llvm 12.
+ */
+ if (__builtin_constant_p(for_write)) {
+ if (for_write)
+ __builtin_prefetch(address, true);
+ else
+ __builtin_prefetch(address, false);
+ }
+}
+
+/**
+ * uds_prefetch_range() - Minimize cache-miss latency by attempting to move a range of addresses
+ * into a CPU cache before they are accessed.
+ *
+ * @start: the starting address to fetch (may be invalid)
+ * @size: the number of bytes in the address range
+ * @for_write: must be constant at compile time--false if for reading, true if for writing
+ */
+static inline void uds_prefetch_range(const void *start, unsigned int size,
+ bool for_write)
+{
+ /*
+ * Count the number of cache lines to fetch, allowing for the address range to span an
+ * extra cache line boundary due to address alignment.
+ */
+ const char *address = (const char *) start;
+ unsigned int offset = ((uintptr_t) address % L1_CACHE_BYTES);
+ unsigned int cache_lines = (1 + ((size + offset) / L1_CACHE_BYTES));
+
+ while (cache_lines-- > 0) {
+ uds_prefetch_address(address, for_write);
+ address += L1_CACHE_BYTES;
+ }
+}
+
+#endif /* UDS_CPU_H */