From: Mathieu Desnoyers Date: Mon, 11 Jul 2011 21:14:08 +0000 (-0400) Subject: rculfhash: diminish index table memory consumption X-Git-Tag: v0.7.0~43^2~199 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=24365af70940dac62e3910e566e91f549a045423;p=userspace-rcu.git rculfhash: diminish index table memory consumption - introduce log2 rcu table for resize. - pull the dummy nodes into invariant per-log2-level tables. Signed-off-by: Mathieu Desnoyers --- diff --git a/rculfhash.c b/rculfhash.c index 0c433e5..606f46e 100644 --- a/rculfhash.c +++ b/rculfhash.c @@ -38,7 +38,7 @@ #include #include -#define DEBUG /* Test */ +//#define DEBUG /* Test */ #ifdef DEBUG #define dbg_printf(args...) printf(args) @@ -67,7 +67,7 @@ struct rcu_table { unsigned long resize_target; int resize_initiated; struct rcu_head head; - struct rcu_ht_node *tbl[0]; + struct _rcu_ht_node *tbl[0]; }; struct rcu_ht { @@ -144,30 +144,138 @@ unsigned long bit_reverse_ulong(unsigned long v) } /* - * Algorithm to find the log2 of a 32-bit unsigned integer. - * source: http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup - * Originally from Public Domain. + * fls: returns the position of the most significant bit. + * Returns 0 if no bit is set, else returns the position of the most + * significant bit (from 1 to 32 on 32-bit, from 1 to 64 on 64-bit). */ -static const char LogTable256[256] = +#if defined(__i386) || defined(__x86_64) +static inline +unsigned int fls_u32(uint32_t x) +{ + int r; + + asm("bsrl %1,%0\n\t" + "jnz 1f\n\t" + "movl $-1,%0\n\t" + "1:\n\t" + : "=r" (r) : "rm" (x)); + return r + 1; +} +#define HAS_FLS_U32 +#endif + +#if defined(__x86_64) +static inline +unsigned int fls_u64(uint64_t x) { -#define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n - -1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, - LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6), - LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7) -}; + long r; -uint32_t log2_u32(uint32_t v) + asm("bsrq %1,%0\n\t" + "jnz 1f\n\t" + "movq $-1,%0\n\t" + "1:\n\t" + : "=r" (r) : "rm" (x)); + return r + 1; +} +#define HAS_FLS_U64 +#endif + +#ifndef HAS_FLS_U64 +static __attribute__((unused)) +unsigned int fls_u64(uint64_t x) { - uint32_t t, tt; + unsigned int r = 64; + + if (!x) + return 0; - if ((tt = (v >> 16))) - return (t = (tt >> 8)) - ? 24 + LogTable256[t] - : 16 + LogTable256[tt]; - else - return (t = (v >> 8)) - ? 8 + LogTable256[t] - : LogTable256[v]; + if (!(x & 0xFFFFFFFF00000000ULL)) { + x <<= 32; + r -= 32; + } + if (!(x & 0xFFFF000000000000ULL)) { + x <<= 16; + r -= 16; + } + if (!(x & 0xFF00000000000000ULL)) { + x <<= 8; + r -= 8; + } + if (!(x & 0xF000000000000000ULL)) { + x <<= 4; + r -= 4; + } + if (!(x & 0xC000000000000000ULL)) { + x <<= 2; + r -= 2; + } + if (!(x & 0x8000000000000000ULL)) { + x <<= 1; + r -= 1; + } + return r; +} +#endif + +#ifndef HAS_FLS_U32 +static __attribute__((unused)) +unsigned int fls_u32(uint32_t x) +{ + unsigned int r = 32; + + if (!x) + return 0; + if (!(x & 0xFFFF0000U)) { + x <<= 16; + r -= 16; + } + if (!(x & 0xFF000000U)) { + x <<= 8; + r -= 8; + } + if (!(x & 0xF0000000U)) { + x <<= 4; + r -= 4; + } + if (!(x & 0xC0000000U)) { + x <<= 2; + r -= 2; + } + if (!(x & 0x80000000U)) { + x <<= 1; + r -= 1; + } + return r; +} +#endif + +unsigned int fls_ulong(unsigned long x) +{ +#if (CAA_BITS_PER_lONG == 32) + return fls_u32(x); +#else + return fls_u64(x); +#endif +} + +int get_count_order_u32(uint32_t x) +{ + int order; + + order = fls_u32(x) - 1; + if (x & (x - 1)) + order++; + return order; +} + +int get_count_order_ulong(unsigned long x) +{ + int order; + + order = fls_ulong(x) - 1; + if (x & (x - 1)) + order++; + return order; } static @@ -177,9 +285,12 @@ static void check_resize(struct rcu_ht *ht, struct rcu_table *t, uint32_t chain_len) { + if (chain_len > 100) + dbg_printf("rculfhash: WARNING: large chain length: %u.\n", + chain_len); if (chain_len >= CHAIN_LEN_RESIZE_THRESHOLD) ht_resize_lazy(ht, t, - log2_u32(chain_len - CHAIN_LEN_TARGET - 1)); + get_count_order_u32(chain_len - CHAIN_LEN_TARGET + 1)); } static @@ -265,7 +376,8 @@ struct rcu_ht_node *_ht_add(struct rcu_ht *ht, struct rcu_table *t, { struct rcu_ht_node *iter_prev, *iter, *next, *new_node, *new_next, *dummy_node; - unsigned long hash; + struct _rcu_ht_node *lookup; + unsigned long hash, index, order; if (!t->size) { assert(dummy); @@ -280,7 +392,10 @@ struct rcu_ht_node *_ht_add(struct rcu_ht *ht, struct rcu_table *t, * iter_prev points to the non-removed node prior to the * insert location. */ - iter_prev = rcu_dereference(t->tbl[hash & (t->size - 1)]); + index = hash & (t->size - 1); + order = get_count_order_ulong(index + 1); + lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + iter_prev = (struct rcu_ht_node *) lookup; /* We can always skip the dummy node initially */ iter = rcu_dereference(iter_prev->p.next); assert(iter_prev->p.reverse_hash <= node->p.reverse_hash); @@ -299,7 +414,8 @@ struct rcu_ht_node *_ht_add(struct rcu_ht *ht, struct rcu_table *t, clear_flag(iter)->key_len)) return clear_flag(iter); /* Only account for identical reverse hash once */ - if (iter_prev->p.reverse_hash != clear_flag(iter)->p.reverse_hash) + if (iter_prev->p.reverse_hash != clear_flag(iter)->p.reverse_hash + && !is_dummy(next)) check_resize(ht, t, ++chain_len); iter_prev = clear_flag(iter); iter = next; @@ -332,7 +448,10 @@ struct rcu_ht_node *_ht_add(struct rcu_ht *ht, struct rcu_table *t, } gc_end: /* Garbage collect logically removed nodes in the bucket */ - dummy_node = rcu_dereference(t->tbl[hash & (t->size - 1)]); + index = hash & (t->size - 1); + order = get_count_order_ulong(index + 1); + lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + dummy_node = (struct rcu_ht_node *) lookup; _ht_gc_bucket(dummy_node, node); return node; } @@ -341,8 +460,9 @@ static int _ht_remove(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node) { struct rcu_ht_node *dummy, *next, *old; + struct _rcu_ht_node *lookup; int flagged = 0; - unsigned long hash; + unsigned long hash, index, order; /* logically delete the node */ old = rcu_dereference(node->p.next); @@ -364,7 +484,10 @@ int _ht_remove(struct rcu_ht *ht, struct rcu_table *t, struct rcu_ht_node *node) * if found. */ hash = bit_reverse_ulong(node->p.reverse_hash); - dummy = rcu_dereference(t->tbl[hash & (t->size - 1)]); + index = hash & (t->size - 1); + order = get_count_order_ulong(index + 1); + lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + dummy = (struct rcu_ht_node *) lookup; _ht_gc_bucket(dummy, node); end: /* @@ -380,20 +503,34 @@ end: static void init_table(struct rcu_ht *ht, struct rcu_table *t, - unsigned long first, unsigned long len) -{ - unsigned long i, end; - - end = first + len; - for (i = first; i < end; i++) { - /* Update table size when power of two */ - if (i != 0 && !(i & (i - 1))) - t->size = i; - t->tbl[i] = calloc(1, sizeof(struct _rcu_ht_node)); - t->tbl[i]->p.reverse_hash = bit_reverse_ulong(i); - (void) _ht_add(ht, t, t->tbl[i], 0, 1); + unsigned long first_order, unsigned long len_order) +{ + unsigned long i, end_order; + + dbg_printf("rculfhash: init table: first_order %lu end_order %lu\n", + first_order, first_order + len_order); + end_order = first_order + len_order; + t->size = !first_order ? 0 : (1UL << (first_order - 1)); + for (i = first_order; i < end_order; i++) { + unsigned long j, len; + + len = !i ? 1 : 1UL << (i - 1); + dbg_printf("rculfhash: init order %lu len: %lu\n", i, len); + t->tbl[i] = calloc(len, sizeof(struct _rcu_ht_node)); + for (j = 0; j < len; j++) { + dbg_printf("rculfhash: init entry: i %lu j %lu hash %lu\n", + i, j, !i ? 0 : (1UL << (i - 1)) + j); + struct rcu_ht_node *new_node = + (struct rcu_ht_node *) &t->tbl[i][j]; + new_node->p.reverse_hash = + bit_reverse_ulong(!i ? 0 : (1UL << (i - 1)) + j); + (void) _ht_add(ht, t, new_node, 0, 1); + } + /* Update table size */ + t->size = !i ? 1 : (1UL << i); + dbg_printf("rculfhash: init new size: %lu\n", t->size); } - t->resize_target = t->size = end; + t->resize_target = t->size; t->resize_initiated = 0; } @@ -405,6 +542,7 @@ struct rcu_ht *ht_new(ht_hash_fct hash_fct, void (*func)(struct rcu_head *head))) { struct rcu_ht *ht; + unsigned long order; ht = calloc(1, sizeof(struct rcu_ht)); ht->hash_fct = hash_fct; @@ -414,11 +552,12 @@ struct rcu_ht *ht_new(ht_hash_fct hash_fct, ht->in_progress_resize = 0; /* this mutex should not nest in read-side C.S. */ pthread_mutex_init(&ht->resize_mutex, NULL); + order = get_count_order_ulong(max(init_size, 1)) + 1; ht->t = calloc(1, sizeof(struct rcu_table) - + (max(init_size, 1) * sizeof(struct rcu_ht_node *))); + + (order * sizeof(struct _rcu_ht_node *))); ht->t->size = 0; pthread_mutex_lock(&ht->resize_mutex); - init_table(ht, ht->t, 0, max(init_size, 1)); + init_table(ht, ht->t, 0, order); pthread_mutex_unlock(&ht->resize_mutex); return ht; } @@ -427,13 +566,19 @@ struct rcu_ht_node *ht_lookup(struct rcu_ht *ht, void *key, size_t key_len) { struct rcu_table *t; struct rcu_ht_node *node, *next; - unsigned long hash, reverse_hash; + struct _rcu_ht_node *lookup; + unsigned long hash, reverse_hash, index, order; hash = ht->hash_fct(key, key_len, ht->hash_seed); reverse_hash = bit_reverse_ulong(hash); t = rcu_dereference(ht->t); - node = rcu_dereference(t->tbl[hash & (t->size - 1)]); + index = hash & (t->size - 1); + order = get_count_order_ulong(index + 1); + lookup = &t->tbl[order][index & ((1UL << (order - 1)) - 1)]; + dbg_printf("rculfhash: lookup hash %lu index %lu order %lu aridx %lu\n", + hash, index, order, index & ((1UL << (order - 1)) - 1)); + node = (struct rcu_ht_node *) lookup; for (;;) { if (unlikely(!node)) break; @@ -490,11 +635,13 @@ int ht_delete_dummy(struct rcu_ht *ht) { struct rcu_table *t; struct rcu_ht_node *node; - unsigned long i; + struct _rcu_ht_node *lookup; + unsigned long order, i; t = ht->t; /* Check that the table is empty */ - node = t->tbl[0]; + lookup = &t->tbl[0][0]; + node = (struct rcu_ht_node *) lookup; do { node = clear_flag(node)->p.next; if (!is_dummy(node)) @@ -502,9 +649,17 @@ int ht_delete_dummy(struct rcu_ht *ht) assert(!is_removed(node)); } while (clear_flag(node)); /* Internal sanity check: all nodes left should be dummy */ - for (i = 0; i < t->size; i++) { - assert(is_dummy(t->tbl[i]->p.next)); - free(t->tbl[i]); + for (order = 0; order < get_count_order_ulong(t->size) + 1; order++) { + unsigned long len; + + len = !order ? 1 : 1UL << (order - 1); + for (i = 0; i < len; i++) { + dbg_printf("rculfhash: delete order %lu i %lu hash %lu\n", + order, i, + bit_reverse_ulong(t->tbl[order][i].reverse_hash)); + assert(is_dummy(t->tbl[order][i].next)); + } + free(t->tbl[order]); } return 0; } @@ -534,13 +689,16 @@ void ht_count_nodes(struct rcu_ht *ht, { struct rcu_table *t; struct rcu_ht_node *node, *next; + struct _rcu_ht_node *lookup; + unsigned long nr_dummy = 0; *count = 0; *removed = 0; t = rcu_dereference(ht->t); - /* Check that the table is empty */ - node = rcu_dereference(t->tbl[0]); + /* Count non-dummy nodes in the table */ + lookup = &t->tbl[0][0]; + node = (struct rcu_ht_node *) lookup; do { next = rcu_dereference(node->p.next); if (is_removed(next)) { @@ -548,8 +706,11 @@ void ht_count_nodes(struct rcu_ht *ht, (*removed)++; } else if (!is_dummy(next)) (*count)++; + else + (nr_dummy)++; node = clear_flag(next); } while (node); + dbg_printf("rculfhash: number of dummy nodes: %lu\n", nr_dummy); } static @@ -564,23 +725,25 @@ void ht_free_table_cb(struct rcu_head *head) static void _do_ht_resize(struct rcu_ht *ht) { - unsigned long new_size, old_size; + unsigned long new_size, old_size, old_order, new_order; struct rcu_table *new_t, *old_t; old_t = ht->t; old_size = old_t->size; + old_order = get_count_order_ulong(old_size) + 1; new_size = CMM_LOAD_SHARED(old_t->resize_target); - dbg_printf("rculfhash: resize from %lu to %lu buckets\n", - old_size, new_size); if (old_size == new_size) return; + new_order = get_count_order_ulong(new_size) + 1; + dbg_printf("rculfhash: resize from %lu (order %lu) to %lu (order %lu) buckets\n", + old_size, old_order, new_size, new_order); new_t = malloc(sizeof(struct rcu_table) - + (new_size * sizeof(struct rcu_ht_node *))); + + (new_order * sizeof(struct _rcu_ht_node *))); assert(new_size > old_size); memcpy(&new_t->tbl, &old_t->tbl, - old_size * sizeof(struct rcu_ht_node *)); - init_table(ht, new_t, old_size, new_size - old_size); + old_order * sizeof(struct _rcu_ht_node *)); + init_table(ht, new_t, old_order, new_order - old_order); /* Changing table and size atomically wrt lookups */ rcu_assign_pointer(ht->t, new_t); ht->ht_call_rcu(&old_t->head, ht_free_table_cb);