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dpif-netdev: Refactor generic implementation

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This commit refactors the generic implementation. The
goal of this refactor is to simplify the code to enable
"specialization" of the functions at compile time.

Given compile-time optimizations, the compiler is able
to unroll loops, and create optimized code sequences due
to compile time knowledge of loop-trip counts.

In order to enable these compiler optimizations, we must
refactor the code to pass the loop-trip counts to functions
as compile time constants.

This patch allows the number of miniflow-bits set per "unit"
in the miniflow to be passed around as a function argument.

Note that this patch does NOT yet take advantage of doing so,
this is only a refactor to enable it in the next patches.

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Tested-by: Malvika Gupta <malvika.gupta@arm.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>
This commit is contained in:
Harry van Haaren
2019-07-18 14:03:05 +01:00
committed by Ian Stokes
parent 92c7c870d6
commit a0b36b3924
3 changed files with 263 additions and 38 deletions
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238
lib/dpif-netdev-lookup-generic.c
View File

@@ -27,61 +27,217 @@
#include "dpif-netdev-perf.h"
#include "dpif-provider.h"
#include "flow.h"
#include "ovs-thread.h"
#include "packets.h"
#include "pvector.h"
/* Returns a hash value for the bits of 'key' where there are 1-bits in
* 'mask'. */
static inline uint32_t
netdev_flow_key_hash_in_mask(const struct netdev_flow_key *key,
const struct netdev_flow_key *mask)
{
const uint64_t *p = miniflow_get_values(&mask->mf);
uint32_t hash = 0;
uint64_t value;
VLOG_DEFINE_THIS_MODULE(dpif_lookup_generic);
NETDEV_FLOW_KEY_FOR_EACH_IN_FLOWMAP (value, key, mask->mf.map) {
hash = hash_add64(hash, value & *p);
p++;
/* Lookup functions below depends on the internal structure of flowmap. */
BUILD_ASSERT_DECL(FLOWMAP_UNITS == 2);
struct block_array {
uint32_t count; /* Number of items allocated in 'blocks' */
uint64_t blocks[];
};
DEFINE_PER_THREAD_MALLOCED_DATA(struct block_array *, block_array);
static inline uint64_t *
get_blocks_scratch(uint32_t required_count)
{
struct block_array *array = block_array_get();
/* Check if this thread already has a large enough array allocated.
* This is a predictable and unlikely branch, as it occurs only once at
* startup, or if a subtable with higher block count is added.
*/
if (OVS_UNLIKELY(!array || array->count < required_count)) {
array = xrealloc(array, sizeof *array +
(required_count * sizeof array->blocks[0]));
array->count = required_count;
block_array_set_unsafe(array);
VLOG_DBG("Block array resized to %"PRIu32, required_count);
}
return hash_finish(hash, (p - miniflow_get_values(&mask->mf)) * 8);
return &array->blocks[0];
}
uint32_t
dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
uint32_t keys_map,
const struct netdev_flow_key *keys[],
struct dpcls_rule **rules)
static inline void
netdev_flow_key_flatten_unit(const uint64_t *pkt_blocks,
const uint64_t *tbl_blocks,
const uint64_t *mf_masks,
uint64_t *blocks_scratch,
const uint64_t pkt_mf_bits,
const uint32_t count)
{
int i;
uint32_t found_map;
uint32_t i;
/* Compute hashes for the remaining keys. Each search-key is
* masked with the subtable's mask to avoid hashing the wildcarded
* bits. */
uint32_t hashes[NETDEV_MAX_BURST];
ULLONG_FOR_EACH_1 (i, keys_map) {
hashes[i] = netdev_flow_key_hash_in_mask(keys[i], &subtable->mask);
for (i = 0; i < count; i++) {
uint64_t mf_mask = mf_masks[i];
/* Calculate the block index for the packet metadata. */
uint64_t idx_bits = mf_mask & pkt_mf_bits;
const uint32_t pkt_idx = count_1bits(idx_bits);
/* Check if the packet has the subtable miniflow bit set. If yes, the
* block at the above pkt_idx will be stored, otherwise it is masked
* out to be zero.
*/
uint64_t pkt_has_mf_bit = (mf_mask + 1) & pkt_mf_bits;
uint64_t no_bit = ((!pkt_has_mf_bit) > 0) - 1;
/* Mask packet block by table block, and mask to zero if packet
* doesn't actually contain this block of metadata.
*/
blocks_scratch[i] = pkt_blocks[pkt_idx] & tbl_blocks[i] & no_bit;
}
}
/* This function takes a packet, and subtable and writes an array of uint64_t
* blocks. The blocks contain the metadata that the subtable matches on, in
* the same order as the subtable, allowing linear iteration over the blocks.
*
* To calculate the blocks contents, the netdev_flow_key_flatten_unit function
* is called twice, once for each "unit" of the miniflow. This call can be
* inlined by the compiler for performance.
*
* Note that the u0_count and u1_count variables can be compile-time constants,
* allowing the loop in the inlined flatten_unit() function to be compile-time
* unrolled, or possibly removed totally by unrolling by the loop iterations.
* The compile time optimizations enabled by this design improves performance.
*/
static inline void
netdev_flow_key_flatten(const struct netdev_flow_key *key,
const struct netdev_flow_key *mask,
const uint64_t *mf_masks,
uint64_t *blocks_scratch,
const uint32_t u0_count,
const uint32_t u1_count)
{
/* Load mask from subtable, mask with packet mf, popcount to get idx. */
const uint64_t *pkt_blocks = miniflow_get_values(&key->mf);
const uint64_t *tbl_blocks = miniflow_get_values(&mask->mf);
/* Packet miniflow bits to be masked by pre-calculated mf_masks. */
const uint64_t pkt_bits_u0 = key->mf.map.bits[0];
const uint32_t pkt_bits_u0_pop = count_1bits(pkt_bits_u0);
const uint64_t pkt_bits_u1 = key->mf.map.bits[1];
/* Unit 0 flattening */
netdev_flow_key_flatten_unit(&pkt_blocks[0],
&tbl_blocks[0],
&mf_masks[0],
&blocks_scratch[0],
pkt_bits_u0,
u0_count);
/* Unit 1 flattening:
* Move the pointers forward in the arrays based on u0 offsets, NOTE:
* 1) pkt blocks indexed by actual popcount of u0, which is NOT always
* the same as the amount of bits set in the subtable.
* 2) mf_masks, tbl_block and blocks_scratch are all "flat" arrays, so
* the index is always u0_count.
*/
netdev_flow_key_flatten_unit(&pkt_blocks[pkt_bits_u0_pop],
&tbl_blocks[u0_count],
&mf_masks[u0_count],
&blocks_scratch[u0_count],
pkt_bits_u1,
u1_count);
}
/* Compares a rule and the blocks representing a key, returns 1 on a match. */
static inline uint64_t
netdev_rule_matches_key(const struct dpcls_rule *rule,
const uint32_t mf_bits_total,
const uint64_t *blocks_scratch)
{
const uint64_t *keyp = miniflow_get_values(&rule->flow.mf);
const uint64_t *maskp = miniflow_get_values(&rule->mask->mf);
uint64_t not_match = 0;
for (int i = 0; i < mf_bits_total; i++) {
not_match |= (blocks_scratch[i] & maskp[i]) != keyp[i];
}
/* Lookup. */
/* Invert result to show match as 1. */
return !not_match;
}
/* Const prop version of the function: note that mf bits total and u0 are
* explicitly passed in here, while they're also available at runtime from the
* subtable pointer. By making them compile time, we enable the compiler to
* unroll loops and flatten out code-sequences based on the knowledge of the
* mf_bits_* compile time values. This results in improved performance.
*
* Note: this function is marked with ALWAYS_INLINE to ensure the compiler
* inlines the below code, and then uses the compile time constants to make
* specialized versions of the runtime code. Without ALWAYS_INLINE, the
* compiler might decide to not inline, and performance will suffer.
*/
static inline uint32_t ALWAYS_INLINE
lookup_generic_impl(struct dpcls_subtable *subtable,
uint32_t keys_map,
const struct netdev_flow_key *keys[],
struct dpcls_rule **rules,
const uint32_t bit_count_u0,
const uint32_t bit_count_u1)
{
const uint32_t n_pkts = count_1bits(keys_map);
ovs_assert(NETDEV_MAX_BURST >= n_pkts);
uint32_t hashes[NETDEV_MAX_BURST];
const uint32_t bit_count_total = bit_count_u0 + bit_count_u1;
const uint32_t block_count_required = bit_count_total * NETDEV_MAX_BURST;
uint64_t *mf_masks = subtable->mf_masks;
int i;
/* Blocks scratch is an optimization to re-use the same packet miniflow
* block data when doing rule-verify. This reduces work done during lookup
* and hence improves performance. The blocks_scratch array is stored as a
* thread local variable, as each thread requires its own blocks memory.
*/
uint64_t *blocks_scratch = get_blocks_scratch(block_count_required);
/* Flatten the packet metadata into the blocks_scratch[] using subtable. */
ULLONG_FOR_EACH_1 (i, keys_map) {
netdev_flow_key_flatten(keys[i],
&subtable->mask,
mf_masks,
&blocks_scratch[i * bit_count_total],
bit_count_u0,
bit_count_u1);
}
/* Hash the now linearized blocks of packet metadata. */
ULLONG_FOR_EACH_1 (i, keys_map) {
uint64_t *block_ptr = &blocks_scratch[i * bit_count_total];
uint32_t hash = hash_add_words64(0, block_ptr, bit_count_total);
hashes[i] = hash_finish(hash, bit_count_total * 8);
}
/* Lookup: this returns a bitmask of packets where the hash table had
* an entry for the given hash key. Presence of a hash key does not
* guarantee matching the key, as there can be hash collisions.
*/
uint32_t found_map;
const struct cmap_node *nodes[NETDEV_MAX_BURST];
found_map = cmap_find_batch(&subtable->rules, keys_map, hashes, nodes);
/* Check results. When the i-th bit of found_map is set, it means
* that a set of nodes with a matching hash value was found for the
* i-th search-key. Due to possible hash collisions we need to check
* which of the found rules, if any, really matches our masked
* search-key. */
/* Verify that packet actually matched rule. If not found, a hash
* collision has taken place, so continue searching with the next node.
*/
ULLONG_FOR_EACH_1 (i, found_map) {
struct dpcls_rule *rule;
CMAP_NODE_FOR_EACH (rule, cmap_node, nodes[i]) {
if (OVS_LIKELY(dpcls_rule_matches_key(rule, keys[i]))) {
const uint32_t cidx = i * bit_count_total;
uint32_t match = netdev_rule_matches_key(rule, bit_count_total,
&blocks_scratch[cidx]);
if (OVS_LIKELY(match)) {
rules[i] = rule;
/* Even at 20 Mpps the 32-bit hit_cnt cannot wrap
* within one second optimization interval. */
subtable->hit_cnt++;
goto next;
}
@@ -96,3 +252,15 @@ dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
return found_map;
}
/* Generic lookup function that uses runtime provided mf bits for iterating. */
uint32_t
dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
uint32_t keys_map,
const struct netdev_flow_key *keys[],
struct dpcls_rule **rules)
{
return lookup_generic_impl(subtable, keys_map, keys, rules,
subtable->mf_bits_set_unit0,
subtable->mf_bits_set_unit1);
}

12
lib/dpif-netdev-private.h
View File

@@ -60,7 +60,7 @@ uint32_t (*dpcls_subtable_lookup_func)(struct dpcls_subtable *subtable,
const struct netdev_flow_key *keys[],
struct dpcls_rule **rules);
/* Prototype for generic lookup func, using same code path as before. */
/* Prototype for generic lookup func, using generic scalar code path. */
uint32_t
dpcls_subtable_lookup_generic(struct dpcls_subtable *subtable,
uint32_t keys_map,
@@ -77,12 +77,22 @@ struct dpcls_subtable {
uint32_t hit_cnt; /* Number of match hits in subtable in current
optimization interval. */
/* Miniflow fingerprint that the subtable matches on. The miniflow "bits"
* are used to select the actual dpcls lookup implementation at subtable
* creation time.
*/
uint8_t mf_bits_set_unit0;
uint8_t mf_bits_set_unit1;
/* The lookup function to use for this subtable. If there is a known
* property of the subtable (eg: only 3 bits of miniflow metadata is
* used for the lookup) then this can point at an optimized version of
* the lookup function for this particular subtable. */
dpcls_subtable_lookup_func lookup_func;
/* Caches the masks to match a packet to, reducing runtime calculations. */
uint64_t *mf_masks;
struct netdev_flow_key mask; /* Wildcards for fields (const). */
/* 'mask' must be the last field, additional space is allocated here. */
};

51
lib/dpif-netdev.c
View File

@@ -7649,6 +7649,7 @@ static void
dpcls_subtable_destroy_cb(struct dpcls_subtable *subtable)
{
cmap_destroy(&subtable->rules);
ovsrcu_postpone(free, subtable->mf_masks);
ovsrcu_postpone(free, subtable);
}
@@ -7701,7 +7702,17 @@ dpcls_create_subtable(struct dpcls *cls, const struct netdev_flow_key *mask)
subtable->hit_cnt = 0;
netdev_flow_key_clone(&subtable->mask, mask);
/* Decide which hash/lookup/verify function to use. */
/* The count of bits in the mask defines the space required for masks.
* Then call gen_masks() to create the appropriate masks, avoiding the cost
* of doing runtime calculations. */
uint32_t unit0 = count_1bits(mask->mf.map.bits[0]);
uint32_t unit1 = count_1bits(mask->mf.map.bits[1]);
subtable->mf_bits_set_unit0 = unit0;
subtable->mf_bits_set_unit1 = unit1;
subtable->mf_masks = xmalloc(sizeof(uint64_t) * (unit0 + unit1));
netdev_flow_key_gen_masks(mask, subtable->mf_masks, unit0, unit1);
/* Assign the generic lookup - this works with any miniflow fingerprint. */
subtable->lookup_func = dpcls_subtable_lookup_generic;
cmap_insert(&cls->subtables_map, &subtable->cmap_node, mask->hash);
@@ -7846,6 +7857,43 @@ dpcls_remove(struct dpcls *cls, struct dpcls_rule *rule)
}
}
/* Inner loop for mask generation of a unit, see netdev_flow_key_gen_masks. */
static inline void
netdev_flow_key_gen_mask_unit(uint64_t iter,
const uint64_t count,
uint64_t *mf_masks)
{
int i;
for (i = 0; i < count; i++) {
uint64_t lowest_bit = (iter & -iter);
iter &= ~lowest_bit;
mf_masks[i] = (lowest_bit - 1);
}
/* Checks that count has covered all bits in the iter bitmap. */
ovs_assert(iter == 0);
}
/* Generate a mask for each block in the miniflow, based on the bits set. This
* allows easily masking packets with the generated array here, without
* calculations. This replaces runtime-calculating the masks.
* @param key The table to generate the mf_masks for
* @param mf_masks Pointer to a u64 array of at least *mf_bits* in size
* @param mf_bits_total Number of bits set in the whole miniflow (both units)
* @param mf_bits_unit0 Number of bits set in unit0 of the miniflow
*/
void
netdev_flow_key_gen_masks(const struct netdev_flow_key *tbl,
uint64_t *mf_masks,
const uint32_t mf_bits_u0,
const uint32_t mf_bits_u1)
{
uint64_t iter_u0 = tbl->mf.map.bits[0];
uint64_t iter_u1 = tbl->mf.map.bits[1];
netdev_flow_key_gen_mask_unit(iter_u0, mf_bits_u0, &mf_masks[0]);
netdev_flow_key_gen_mask_unit(iter_u1, mf_bits_u1, &mf_masks[mf_bits_u0]);
}
/* Returns true if 'target' satisfies 'key' in 'mask', that is, if each 1-bit
* in 'mask' the values in 'key' and 'target' are the same. */
bool
@@ -7886,7 +7934,6 @@ dpcls_lookup(struct dpcls *cls, const struct netdev_flow_key *keys[],
BUILD_ASSERT_DECL(MAP_BITS >= NETDEV_MAX_BURST);
struct dpcls_subtable *subtable;
uint32_t keys_map = TYPE_MAXIMUM(uint32_t); /* Set all bits. */
if (cnt != MAP_BITS) {