On 11/22/2011 05:58 PM, Mathieu Desnoyers wrote:
> * Lai Jiangshan ([email protected]) wrote:
>> Fast path is not changed.
>> It will slow down very little for slow path.
>
> it cleans up the code, so it's generally fine with me. There is just one
> part that I don't understand, see below,
>
>>
>> Signed-off-by: Lai Jiangshan <[email protected]>
>> ---
>> rculfhash.c | 100
>> +++++++++++++++++++++++++++-------------------------------
>> 1 files changed, 47 insertions(+), 53 deletions(-)
>>
>> diff --git a/rculfhash.c b/rculfhash.c
>> index bda3bd6..b0c7de5 100644
>> --- a/rculfhash.c
>> +++ b/rculfhash.c
>> @@ -755,18 +755,14 @@ unsigned long
>> _uatomic_xchg_monotonic_increase(unsigned long *ptr,
>> return old2;
>> }
>>
>> -static
>> -struct cds_lfht_node *lookup_bucket(struct cds_lfht *ht, unsigned long size,
>> - unsigned long hash)
>> +static inline
>> +struct cds_lfht_node *bucket_at(struct cds_lfht *ht, unsigned long index)
>> {
>> - unsigned long index, order;
>> -
>> - assert(size > 0);
>> - index = hash & (size - 1);
>> + unsigned long order;
>>
>> - if (index < ht->min_alloc_size) {
>> - dbg_printf("lookup hash %lu index %lu order 0 aridx 0\n",
>> - hash, index);
>> + if ((__builtin_constant_p(index) && index == 0)
>> + || index < ht->min_alloc_size) {
>> + dbg_printf("bucket index %lu order 0 aridx 0\n", index);
>> return &ht->t.tbl[0]->nodes[index];
>> }
>> /*
>> @@ -775,11 +771,19 @@ struct cds_lfht_node *lookup_bucket(struct cds_lfht
>> *ht, unsigned long size,
>> * get_count_order_ulong.
>> */
>> order = fls_ulong(index);
>> - dbg_printf("lookup hash %lu index %lu order %lu aridx %lu\n",
>> - hash, index, order, index & ((1UL << (order - 1)) - 1));
>> + dbg_printf("bucket index %lu order %lu aridx %lu\n",
>> + index, order, index & ((1UL << (order - 1)) - 1));
>> return &ht->t.tbl[order]->nodes[index & ((1UL << (order - 1)) - 1)];
>> }
>>
>> +static inline
>> +struct cds_lfht_node *lookup_bucket(struct cds_lfht *ht, unsigned long size,
>> + unsigned long hash)
>> +{
>> + assert(size > 0);
>> + return bucket_at(ht, hash & (size - 1));
>> +}
>> +
>> /*
>> * Remove all logically deleted nodes from a bucket up to a certain node
>> key.
>> */
>> @@ -1105,19 +1109,18 @@ static
>> void init_table_populate_partition(struct cds_lfht *ht, unsigned long i,
>> unsigned long start, unsigned long len)
>> {
>> - unsigned long j;
>> + unsigned long j, size = 1UL << (i - 1);
>>
>> assert(i > ht->min_alloc_order);
>> ht->cds_lfht_rcu_read_lock();
>> - for (j = start; j < start + len; j++) {
>> - struct cds_lfht_node *new_node = &ht->t.tbl[i]->nodes[j];
>> -
>> - dbg_printf("init populate: i %lu j %lu hash %lu\n",
>> - i, j, (1UL << (i - 1)) + j);
>> - new_node->reverse_hash =
>> - bit_reverse_ulong((1UL << (i - 1)) + j);
>> - _cds_lfht_add(ht, NULL, NULL, 1UL << (i - 1),
>> - new_node, NULL, 1);
>> + for (j = start + size; j < size + start + len; j++) {
>
> Please use "j = size + start; j < size + start + len;"
>
>> + struct cds_lfht_node *new_node = bucket_at(ht, j);
>> +
>> + assert(j >= size && j < (size << 1));
>> + dbg_printf("init populate: order %lu index %lu hash %lu\n",
>> + i, j, j);
>> + new_node->reverse_hash = bit_reverse_ulong(j);
>> + _cds_lfht_add(ht, NULL, NULL, size, new_node, NULL, 1);
>> }
>> ht->cds_lfht_rcu_read_unlock();
>> }
>> @@ -1205,18 +1208,18 @@ static
>> void remove_table_partition(struct cds_lfht *ht, unsigned long i,
>> unsigned long start, unsigned long len)
>> {
>> - unsigned long j;
>> + unsigned long j, size = 1UL << (i - 1);
>>
>> assert(i > ht->min_alloc_order);
>> ht->cds_lfht_rcu_read_lock();
>> - for (j = start; j < start + len; j++) {
>> - struct cds_lfht_node *fini_node = &ht->t.tbl[i]->nodes[j];
>> -
>> - dbg_printf("remove entry: i %lu j %lu hash %lu\n",
>> - i, j, (1UL << (i - 1)) + j);
>> - fini_node->reverse_hash =
>> - bit_reverse_ulong((1UL << (i - 1)) + j);
>> - (void) _cds_lfht_del(ht, 1UL << (i - 1), fini_node, 1);
>> + for (j = size + start; j < size + start + len; j++) {
>> + struct cds_lfht_node *fini_node = bucket_at(ht, j);
>> +
>> + assert(j >= size && j < (size << 1));
>> + dbg_printf("remove entry: order %lu index %lu hash %lu\n",
>> + i, j, j);
>> + fini_node->reverse_hash = bit_reverse_ulong(j);
>> + (void) _cds_lfht_del(ht, size, fini_node, 1);
>> }
>> ht->cds_lfht_rcu_read_unlock();
>> }
>> @@ -1293,14 +1296,15 @@ static
>> void cds_lfht_create_bucket(struct cds_lfht *ht, unsigned long size)
>> {
>> struct cds_lfht_node *prev, *node;
>> - unsigned long order, len, i, j;
>> + unsigned long order, len, i;
>>
>> ht->t.tbl[0] = calloc(1, ht->min_alloc_size * sizeof(struct
>> cds_lfht_node));
>> assert(ht->t.tbl[0]);
>>
>> - dbg_printf("create bucket: order %lu index %lu hash %lu\n", 0, 0, 0);
>> - ht->t.tbl[0]->nodes[0].next = flag_bucket(get_end());
>> - ht->t.tbl[0]->nodes[0].reverse_hash = 0;
>> + dbg_printf("create bucket: order 0 index 0 hash 0\n");
>> + node = bucket_at(ht, 0);
>> + node->next = flag_bucket(get_end());
>> + node->reverse_hash = 0;
>>
>> for (order = 1; order < get_count_order_ulong(size) + 1; order++) {
>> len = 1UL << (order - 1);
>> @@ -1311,22 +1315,15 @@ void cds_lfht_create_bucket(struct cds_lfht *ht,
>> unsigned long size)
>> assert(ht->t.tbl[order]);
>> }
>>
>
> below is the change I fail to understand. I think I'd need to be walked
> through this change with an explanation, which could be added as a
> comment telling what this function is doing.
The "if else if" code simulates the code of "set prev as the bucket with
index=i".
it is "bucket_at(ht, i)".
Now, we are trying to init the node with the hash=(i+len) (which is also
a bucket with index=(i+len)) to the hash table, so this node has to be inserted
after the bucket with index=i. And because there is no other non-bucket node
nor bucket node with larger index inserted, so the bucket node with
index=(i+len)
should be inserted directly linked after the bucket node with index=i.
>
>> - i = 0;
>> - prev = ht->t.tbl[i]->nodes;
>> - for (j = 0; j < len; j++) {
>> - if (j & (j - 1)) { /* Between power of 2 */
>> - prev++;
>> - } else if (j) { /* At each power of 2 */
>> - i++;
>> - prev = ht->t.tbl[i]->nodes;
>> - }
>> + for (i = 0; i < len; i++) {
>> + prev = bucket_at(ht, i);
>> + node = bucket_at(ht, i + len);
>
>
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