[ltt-dev] [PATCH 01/10 round10] introduce bucket_at() and improve readability
Mathieu Desnoyers
mathieu.desnoyers at efficios.com
Wed Nov 23 01:50:35 EST 2011
* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> On 11/22/2011 05:58 PM, Mathieu Desnoyers wrote:
> > * Lai Jiangshan (laijs at cn.fujitsu.com) 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 <laijs at cn.fujitsu.com>
> >> ---
> >> 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.
>
Sounds like a very reasonable explanation to me. Please add this as a
comment block above the function.
Thanks!
Mathieu
>
> >
> >> - 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);
> >
> >
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
More information about the lttng-dev
mailing list