More aggsum optimizations

- Avoid atomic_add() when updating as_lower_bound/as_upper_bound.
Previous code was excessively strong on 64bit systems while not
strong enough on 32bit ones.  Instead introduce and use real
atomic_load() and atomic_store() operations, just an assignments
on 64bit machines, but using proper atomics on 32bit ones to avoid
torn reads/writes.

 - Reduce number of buckets on large systems.  Extra buckets not as
much improve add speed, as hurt reads.  Unlike wmsum for aggsum
reads are still important.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Sponsored-By: iXsystems, Inc.
Closes #12145

2 files changed, 56 insertions, 0 deletions

diff --git a/lib/libspl/asm-generic/atomic.c b/lib/libspl/asm-generic/atomic.c
index 35535ea49..504422b8e 100644
--- a/lib/libspl/asm-generic/atomic.c
+++ b/lib/libspl/asm-generic/atomic.c
@@ -390,6 +390,19 @@ atomic_swap_ptr(volatile void *target, void *bits)
 	return (old);
 }
 
+#ifndef _LP64
+uint64_t
+atomic_load_64(volatile uint64_t *target)
+{
+	return (__atomic_load_n(target, __ATOMIC_RELAXED));
+}
+
+void
+atomic_store_64(volatile uint64_t *target, uint64_t bits)
+{
+	return (__atomic_store_n(target, bits, __ATOMIC_RELAXED));
+}
+#endif
 
 int
 atomic_set_long_excl(volatile ulong_t *target, uint_t value)
diff --git a/lib/libspl/include/atomic.h b/lib/libspl/include/atomic.h
index f8c257f96..8dd1d654a 100644
--- a/lib/libspl/include/atomic.h
+++ b/lib/libspl/include/atomic.h
@@ -246,6 +246,49 @@ extern uint64_t atomic_swap_64(volatile uint64_t *, uint64_t);
 #endif
 
 /*
+ * Atomically read variable.
+ */
+#define	atomic_load_char(p)	(*(volatile uchar_t *)(p))
+#define	atomic_load_short(p)	(*(volatile ushort_t *)(p))
+#define	atomic_load_int(p)	(*(volatile uint_t *)(p))
+#define	atomic_load_long(p)	(*(volatile ulong_t *)(p))
+#define	atomic_load_ptr(p)	(*(volatile __typeof(*p) *)(p))
+#define	atomic_load_8(p)	(*(volatile uint8_t *)(p))
+#define	atomic_load_16(p)	(*(volatile uint16_t *)(p))
+#define	atomic_load_32(p)	(*(volatile uint32_t *)(p))
+#ifdef _LP64
+#define	atomic_load_64(p)	(*(volatile uint64_t *)(p))
+#elif defined(_INT64_TYPE)
+extern uint64_t atomic_load_64(volatile uint64_t *);
+#endif
+
+/*
+ * Atomically write variable.
+ */
+#define	atomic_store_char(p, v)		\
+	(*(volatile uchar_t *)(p) = (uchar_t)(v))
+#define	atomic_store_short(p, v)	\
+	(*(volatile ushort_t *)(p) = (ushort_t)(v))
+#define	atomic_store_int(p, v)		\
+	(*(volatile uint_t *)(p) = (uint_t)(v))
+#define	atomic_store_long(p, v)		\
+	(*(volatile ulong_t *)(p) = (ulong_t)(v))
+#define	atomic_store_ptr(p, v)		\
+	(*(volatile __typeof(*p) *)(p) = (v))
+#define	atomic_store_8(p, v)		\
+	(*(volatile uint8_t *)(p) = (uint8_t)(v))
+#define	atomic_store_16(p, v)		\
+	(*(volatile uint16_t *)(p) = (uint16_t)(v))
+#define	atomic_store_32(p, v)		\
+	(*(volatile uint32_t *)(p) = (uint32_t)(v))
+#ifdef _LP64
+#define	atomic_store_64(p, v)		\
+	(*(volatile uint64_t *)(p) = (uint64_t)(v))
+#elif defined(_INT64_TYPE)
+extern void atomic_store_64(volatile uint64_t *, uint64_t);
+#endif
+
+/*
  * Perform an exclusive atomic bit set/clear on a target.
  * Returns 0 if bit was successfully set/cleared, or -1
  * if the bit was already set/cleared.