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Changed stream list to arrays and optimized stream lookup with SSE2.
The stream list in the SRTP context is now implemented with two arrays: an array of SSRCs and an array of pointers to the streams corresponding to the SSRCs. The streams no longer form a linked list. Stream lookup by SSRC is now performed over the array of SSRCs, which is considerably faster because it is more cache-friendly. Additionally, the lookup is optimized for SSE2, which provides an additional massive speedup with many streams in the list. Although the lookup still has linear complexity, its absolute times are reduced and with tens to hundreds elements are lower or comparable with a typical rb-tree equivalent. Expected speedup of SSE2 version over the previous implementation: SSRCs speedup (scalar) speedup (SSE2) 1 0.39x 0.22x 3 0.57x 0.23x 5 0.69x 0.62x 10 0.77x 1.43x 20 0.86x 2.38x 30 0.87x 3.44x 50 1.13x 6.21x 100 1.25x 8.51x 200 1.30x 9.83x These numbers were obtained on a Core i7 2600K. At small numbers of SSRCs the new algorithm is somewhat slower, but given that the absolute and relative times of the lookup are very small, that slowdown is not very significant.
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‎srtp/srtp.c‎

Lines changed: 197 additions & 34 deletions
Original file line numberDiff line numberDiff line change
@@ -60,13 +60,22 @@
6060
#include "aes_icm_ext.h"
6161
#endif
6262

63+
#include <stddef.h>
64+
#include <string.h>
6365
#include <limits.h>
6466
#ifdef HAVE_NETINET_IN_H
6567
#include <netinet/in.h>
6668
#elif defined(HAVE_WINSOCK2_H)
6769
#include <winsock2.h>
6870
#endif
6971

72+
#if defined(__SSE2__)
73+
#include <emmintrin.h>
74+
#if defined(_MSC_VER)
75+
#include <intrin.h>
76+
#endif
77+
#endif
78+
7079
/* the debug module for srtp */
7180
srtp_debug_module_t mod_srtp = {
7281
0, /* debugging is off by default */
@@ -79,6 +88,16 @@ srtp_debug_module_t mod_srtp = {
7988
#define uint32s_in_rtcp_header 2
8089
#define octets_in_rtp_extn_hdr 4
8190

91+
#ifndef SRTP_NO_STREAM_LIST
92+
static inline uint32_t srtp_stream_list_size(srtp_stream_list_t list);
93+
static srtp_err_status_t srtp_stream_list_reserve(srtp_stream_list_t list,
94+
uint32_t new_capacity);
95+
static uint32_t srtp_stream_list_find(srtp_stream_list_t list, uint32_t ssrc);
96+
static inline srtp_stream_t srtp_stream_list_get_at(srtp_stream_list_t list,
97+
uint32_t pos);
98+
static void srtp_stream_list_remove_at(srtp_stream_list_t list, uint32_t pos);
99+
#endif // SRTP_NO_STREAM_LIST
100+
82101
static srtp_err_status_t srtp_validate_rtp_header(void *rtp_hdr,
83102
int *pkt_octet_len)
84103
{
@@ -3030,18 +3049,31 @@ srtp_err_status_t srtp_remove_stream(srtp_t session, uint32_t ssrc)
30303049
{
30313050
srtp_stream_ctx_t *stream;
30323051
srtp_err_status_t status;
3052+
#if !defined(SRTP_NO_STREAM_LIST)
3053+
uint32_t pos;
3054+
#endif
30333055

30343056
/* sanity check arguments */
3035-
if (session == NULL)
3057+
if (session == NULL) {
30363058
return srtp_err_status_bad_param;
3059+
}
30373060

30383061
/* find and remove stream from the list */
3062+
#if !defined(SRTP_NO_STREAM_LIST)
3063+
pos = srtp_stream_list_find(session->stream_list, ssrc);
3064+
if (pos >= srtp_stream_list_size(session->stream_list))
3065+
return srtp_err_status_no_ctx;
3066+
3067+
stream = srtp_stream_list_get_at(session->stream_list, pos);
3068+
srtp_stream_list_remove_at(session->stream_list, pos);
3069+
#else
30393070
stream = srtp_stream_list_get(session->stream_list, ssrc);
30403071
if (stream == NULL) {
30413072
return srtp_err_status_no_ctx;
30423073
}
30433074

30443075
srtp_stream_list_remove(session->stream_list, stream);
3076+
#endif
30453077

30463078
/* deallocate the stream */
30473079
status = srtp_stream_dealloc(stream, session->stream_template);
@@ -4840,11 +4872,11 @@ srtp_err_status_t srtp_get_stream_roc(srtp_t session,
48404872

48414873
#ifndef SRTP_NO_STREAM_LIST
48424874

4843-
/* in the default implementation, we have an intrusive doubly-linked list */
48444875
typedef struct srtp_stream_list_ctx_t_ {
4845-
/* a stub stream that just holds pointers to the beginning and end of the
4846-
* list */
4847-
srtp_stream_ctx_t data;
4876+
uint32_t *ssrcs;
4877+
srtp_stream_ctx_t **streams;
4878+
uint32_t size;
4879+
uint32_t capacity;
48484880
} srtp_stream_list_ctx_t_;
48494881

48504882
srtp_err_status_t srtp_stream_list_alloc(srtp_stream_list_t *list_ptr)
@@ -4855,73 +4887,204 @@ srtp_err_status_t srtp_stream_list_alloc(srtp_stream_list_t *list_ptr)
48554887
return srtp_err_status_alloc_fail;
48564888
}
48574889

4858-
list->data.next = NULL;
4859-
list->data.prev = NULL;
4860-
48614890
*list_ptr = list;
48624891
return srtp_err_status_ok;
48634892
}
48644893

48654894
srtp_err_status_t srtp_stream_list_dealloc(srtp_stream_list_t list)
48664895
{
48674896
/* list must be empty */
4868-
if (list->data.next) {
4897+
if (list->size != 0u) {
48694898
return srtp_err_status_fail;
48704899
}
4900+
srtp_crypto_free(list->streams);
4901+
srtp_crypto_free(list->ssrcs);
48714902
srtp_crypto_free(list);
48724903
return srtp_err_status_ok;
48734904
}
48744905

4906+
static inline uint32_t srtp_stream_list_size(srtp_stream_list_t list)
4907+
{
4908+
return list->size;
4909+
}
4910+
4911+
static srtp_err_status_t srtp_stream_list_reserve(srtp_stream_list_t list,
4912+
uint32_t new_capacity)
4913+
{
4914+
if (new_capacity > list->capacity) {
4915+
uint32_t *ssrcs;
4916+
srtp_stream_ctx_t **stream_ptrs;
4917+
4918+
if (new_capacity > (UINT32_MAX - 15u))
4919+
return srtp_err_status_alloc_fail;
4920+
4921+
new_capacity = (new_capacity + 15u) & ~((uint32_t)15u);
4922+
4923+
ssrcs = (uint32_t *)srtp_crypto_alloc((size_t)new_capacity *
4924+
sizeof(uint32_t));
4925+
if (!ssrcs)
4926+
return srtp_err_status_alloc_fail;
4927+
stream_ptrs = (srtp_stream_ctx_t **)srtp_crypto_alloc(
4928+
(size_t)new_capacity * sizeof(srtp_stream_ctx_t *));
4929+
if (!stream_ptrs) {
4930+
srtp_crypto_free(ssrcs);
4931+
return srtp_err_status_alloc_fail;
4932+
}
4933+
4934+
if (list->size > 0u) {
4935+
memcpy(ssrcs, list->ssrcs, (size_t)list->size * sizeof(uint32_t));
4936+
memcpy(stream_ptrs, list->streams,
4937+
(size_t)list->size * sizeof(srtp_stream_ctx_t *));
4938+
}
4939+
4940+
srtp_crypto_free(list->ssrcs);
4941+
srtp_crypto_free(list->streams);
4942+
list->streams = stream_ptrs;
4943+
list->ssrcs = ssrcs;
4944+
4945+
list->capacity = new_capacity;
4946+
}
4947+
4948+
return srtp_err_status_ok;
4949+
}
4950+
48754951
srtp_err_status_t srtp_stream_list_insert(srtp_stream_list_t list,
48764952
srtp_stream_t stream)
48774953
{
4878-
/* insert at the head of the list */
4879-
stream->next = list->data.next;
4880-
if (stream->next != NULL) {
4881-
stream->next->prev = stream;
4882-
}
4883-
list->data.next = stream;
4884-
stream->prev = &(list->data);
4954+
uint32_t pos;
4955+
srtp_err_status_t status = srtp_stream_list_reserve(list, list->size + 1u);
4956+
if (status)
4957+
return status;
4958+
pos = list->size++;
4959+
list->ssrcs[pos] = stream->ssrc;
4960+
list->streams[pos] = stream;
48854961

48864962
return srtp_err_status_ok;
48874963
}
48884964

4889-
srtp_stream_t srtp_stream_list_get(srtp_stream_list_t list, uint32_t ssrc)
4965+
static uint32_t srtp_stream_list_find(srtp_stream_list_t list, uint32_t ssrc)
48904966
{
4891-
/* walk down list until ssrc is found */
4892-
srtp_stream_t stream = list->data.next;
4893-
while (stream != NULL) {
4894-
if (stream->ssrc == ssrc) {
4895-
return stream;
4967+
#if defined(__SSE2__)
4968+
const uint32_t *const ssrcs = list->ssrcs;
4969+
const __m128i mm_ssrc = _mm_set1_epi32(ssrc);
4970+
uint32_t pos = 0u, n = (list->size + 7u) & ~(uint32_t)(7u);
4971+
for (uint32_t m = n & ~(uint32_t)(15u); pos < m; pos += 16u) {
4972+
__m128i mm1 = _mm_loadu_si128((const __m128i *)(ssrcs + pos));
4973+
__m128i mm2 = _mm_loadu_si128((const __m128i *)(ssrcs + pos + 4u));
4974+
__m128i mm3 = _mm_loadu_si128((const __m128i *)(ssrcs + pos + 8u));
4975+
__m128i mm4 = _mm_loadu_si128((const __m128i *)(ssrcs + pos + 12u));
4976+
mm1 = _mm_cmpeq_epi32(mm1, mm_ssrc);
4977+
mm2 = _mm_cmpeq_epi32(mm2, mm_ssrc);
4978+
mm3 = _mm_cmpeq_epi32(mm3, mm_ssrc);
4979+
mm4 = _mm_cmpeq_epi32(mm4, mm_ssrc);
4980+
mm1 = _mm_packs_epi32(mm1, mm2);
4981+
mm3 = _mm_packs_epi32(mm3, mm4);
4982+
mm1 = _mm_packs_epi16(mm1, mm3);
4983+
uint32_t mask = _mm_movemask_epi8(mm1);
4984+
if (mask) {
4985+
#if defined(_MSC_VER)
4986+
unsigned long bit_pos;
4987+
_BitScanForward(&bit_pos, mask);
4988+
pos += bit_pos;
4989+
#else
4990+
pos += __builtin_ctz(mask);
4991+
#endif
4992+
4993+
goto done;
4994+
}
4995+
}
4996+
4997+
if (pos < n) {
4998+
__m128i mm1 = _mm_loadu_si128((const __m128i *)(ssrcs + pos));
4999+
__m128i mm2 = _mm_loadu_si128((const __m128i *)(ssrcs + pos + 4u));
5000+
mm1 = _mm_cmpeq_epi32(mm1, mm_ssrc);
5001+
mm2 = _mm_cmpeq_epi32(mm2, mm_ssrc);
5002+
mm1 = _mm_packs_epi32(mm1, mm2);
5003+
5004+
uint32_t mask = _mm_movemask_epi8(mm1);
5005+
if (mask) {
5006+
#if defined(_MSC_VER)
5007+
unsigned long bit_pos;
5008+
_BitScanForward(&bit_pos, mask);
5009+
pos += bit_pos / 2u;
5010+
#else
5011+
pos += __builtin_ctz(mask) / 2u;
5012+
#endif
5013+
goto done;
48965014
}
4897-
stream = stream->next;
5015+
5016+
pos += 8u;
5017+
}
5018+
5019+
done:
5020+
return pos;
5021+
#else
5022+
/* walk down list until ssrc is found */
5023+
uint32_t pos = 0u, n = list->size;
5024+
for (; pos < n; ++pos) {
5025+
if (list->ssrcs[pos] == ssrc)
5026+
break;
48985027
}
48995028

5029+
return pos;
5030+
#endif
5031+
}
5032+
5033+
static inline srtp_stream_t srtp_stream_list_get_at(srtp_stream_list_t list,
5034+
uint32_t pos)
5035+
{
5036+
return list->streams[pos];
5037+
}
5038+
5039+
srtp_stream_t srtp_stream_list_get(srtp_stream_list_t list, uint32_t ssrc)
5040+
{
5041+
uint32_t pos = srtp_stream_list_find(list, ssrc);
5042+
if (pos < list->size)
5043+
return list->streams[pos];
5044+
49005045
/* we haven't found our ssrc, so return a null */
49015046
return NULL;
49025047
}
49035048

4904-
void srtp_stream_list_remove(srtp_stream_list_t list,
4905-
srtp_stream_t stream_to_remove)
5049+
static void srtp_stream_list_remove_at(srtp_stream_list_t list, uint32_t pos)
49065050
{
4907-
(void)list;
5051+
uint32_t tail_size, last_pos;
49085052

4909-
stream_to_remove->prev->next = stream_to_remove->next;
4910-
if (stream_to_remove->next != NULL) {
4911-
stream_to_remove->next->prev = stream_to_remove->prev;
5053+
last_pos = --list->size;
5054+
tail_size = last_pos - pos;
5055+
if (tail_size > 0u) {
5056+
memmove(list->streams + pos, list->streams + pos + 1,
5057+
(size_t)tail_size * sizeof(*list->streams));
5058+
memmove(list->ssrcs + pos, list->ssrcs + pos + 1,
5059+
(size_t)tail_size * sizeof(*list->ssrcs));
49125060
}
5061+
5062+
list->streams[last_pos] = NULL;
5063+
list->ssrcs[last_pos] = 0u;
5064+
}
5065+
5066+
void srtp_stream_list_remove(srtp_stream_list_t list,
5067+
srtp_stream_t stream_to_remove)
5068+
{
5069+
uint32_t pos = srtp_stream_list_find(list, stream_to_remove->ssrc);
5070+
if (pos < list->size)
5071+
srtp_stream_list_remove_at(list, pos);
49135072
}
49145073

49155074
void srtp_stream_list_for_each(srtp_stream_list_t list,
49165075
int (*callback)(srtp_stream_t, void *),
49175076
void *data)
49185077
{
4919-
srtp_stream_t stream = list->data.next;
4920-
while (stream != NULL) {
4921-
srtp_stream_t tmp = stream;
4922-
stream = stream->next;
4923-
if (callback(tmp, data))
5078+
uint32_t size = list->size;
5079+
for (uint32_t i = 0u; i < size;) {
5080+
if (callback(list->streams[i], data))
49245081
break;
5082+
5083+
/* check if the callback removed the current element */
5084+
if (size == list->size)
5085+
++i;
5086+
else
5087+
size = list->size;
49255088
}
49265089
}
49275090

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