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/*************************************************************************
* Copyright (c) 2016-2019, NVIDIA CORPORATION. All rights reserved.
*
* See LICENSE.txt for license information
************************************************************************/
#include "core.h"
#include "devcomm.h"
#include "comm.h"
#include "topo.h"
NCCL_PARAM(Nthreads, "NTHREADS", -2);
NCCL_PARAM(Ll128Nthreads, "LL128_NTHREADS", -2);
static int getNthreads(const char* name, int env, int min, int max, int def) {
int nt = env;
if (nt > 0) {
if (nt % WARP_SIZE != 0) {
WARN("Invalid %s %d (must be a multiple of %d)", name, nt, WARP_SIZE);
nt = max;
} else if (nt > max) {
WARN("Invalid %s %d (maximum %d).", name, nt, max);
nt = max;
} else if (nt < min) {
WARN("Invalid %s %d (minimum %d).", name, nt, min);
nt = min;
}
} else {
nt = def;
}
return nt;
}
ncclResult_t parseList(const char* str, const char* elems[], int nelems, int* list) {
int def, set;
if (str[0] == '^') {
def = 1; set = 0; str++;
} else {
def = 0; set = 1;
}
for (int i=0; i<nelems; i++) list[i] = def;
char* tokStr = strdup(str);
char* tmpStr;
char* token = strtok_r(tokStr, ",", &tmpStr);
while (token) {
for (int i=0; i<nelems; i++)
if (strcasecmp(token, elems[i]) == 0) list[i] = set;
token = strtok_r(NULL, ",", &tmpStr);
}
free(tokStr);
return ncclSuccess;
}
static const char* ncclFuncStr[] = { "Broadcast", "Reduce", "AllGather", "ReduceScatter", "AllReduce" };
static const char* ncclAlgoStr[] = { "Tree", "Ring" };
static const char* ncclProtoStr[] = { "LL", "LL128", "Simple" };
// Latencies in us, Bandwidths in GB/s
// Tree { LL, LL128, Simple } , Ring { LL, LL128, Simple }
static const float baseLat [NCCL_NUM_ALGORITHMS][NCCL_NUM_PROTOCOLS] = { { 4.4, 4.4, 0 }, { 3.6, 3.6, 8.4 } };
// NVLink, PCI, Network
#define NCCL_HW_NVLINK 0
#define NCCL_HW_PCI 1
#define NCCL_HW_NET 2
// Tree/Simple is the latency a 256kB chunk, which is ~ base lat + 256k/12GB/s (+ 256k/12GB/s for the network).
static const float hwLat [3][NCCL_NUM_ALGORITHMS][NCCL_NUM_PROTOCOLS] =
{ /* NVLINK */
{ /* Tree (LL/LL128/Simple)*/ { .5, 1.9, 28 }, /* Ring (LL/LL128/Simple)*/ { .4, 2.5, 5.7 } },
/* PCI */
{ /* Tree (LL/LL128/Simple)*/ { 1.0, 1.9, 28 }, /* Ring (LL/LL128/Simple)*/ { 1.0, 2.5, 5.7 } },
/* NET */
{ /* Tree (LL/LL128/Simple)*/ { 5.0, 7.5, 50 }, /* Ring (LL/LL128/Simple)*/ { .9, 2.5, 6.6 } }
};
// LL128 max BW for the different collectives
static const double ll128MaxBw[NCCL_NUM_FUNCTIONS] = { 113.0, 72.0, 110.0, 91.0, 100.0 };
ncclResult_t ncclSetThresholds(struct ncclComm* comm, int minCompCap, int maxCompCap, struct ncclTopoGraph* treeGraph, struct ncclTopoGraph* ringGraph) {
int simpleDefaultThreads = (treeGraph->speedIntra*treeGraph->nChannels <= 12) ? 256 : NCCL_MAX_NTHREADS;
comm->maxThreads[NCCL_PROTO_SIMPLE] = getNthreads("NCCL_NTHREADS", ncclParamNthreads(), 2*WARP_SIZE, NCCL_MAX_NTHREADS, simpleDefaultThreads);
comm->maxThreads[NCCL_PROTO_LL] = getNthreads("NCCL_NTHREADS", ncclParamNthreads(), 2*WARP_SIZE, NCCL_MAX_NTHREADS, NCCL_MAX_NTHREADS);
comm->maxThreads[NCCL_PROTO_LL128] = getNthreads("NCCL_LL128_NTHREADS", ncclParamLl128Nthreads(), NCCL_LL128_MAX_NTHREADS/4, NCCL_LL128_MAX_NTHREADS, NCCL_LL128_MAX_NTHREADS);
INFO(NCCL_INIT, "Threads per block : %d/%d/%d", comm->maxThreads[NCCL_PROTO_LL], comm->maxThreads[NCCL_PROTO_LL128], comm->maxThreads[NCCL_PROTO_SIMPLE]);
if (comm->nRanks <= 1) return ncclSuccess;
struct ncclTopoGraph* graphs[2] = { treeGraph, ringGraph };
int intraHw[2], hw[2];
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) intraHw[a] = graphs[a]->nvlink ? NCCL_HW_NVLINK : NCCL_HW_PCI;
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) hw[a] = comm->nNodes == 1 ? intraHw[a] : NCCL_HW_NET;
for (int coll=0; coll<NCCL_NUM_FUNCTIONS; coll++) {
int nsteps = coll == ncclCollAllReduce ? 2*(comm->nRanks-1) :
coll == ncclCollReduceScatter || coll == ncclCollAllGather ? comm->nRanks-1 :
comm->nRanks;
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
if (coll != ncclCollAllReduce && a == NCCL_ALGO_TREE) continue;
for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
int speed = comm->nNodes <= 2 ? graphs[a]->speedIntra : graphs[a]->speedInter;
float busBw = graphs[a]->nChannels * speed * 1.0;
// Various model refinements
if (a == NCCL_ALGO_RING && p == NCCL_PROTO_LL) busBw *= 1.0/4.0;
if (a == NCCL_ALGO_RING && p == NCCL_PROTO_LL128) busBw = std::min(busBw*120.0/128.0, ll128MaxBw[coll]);
if (a == NCCL_ALGO_TREE) busBw = std::min(busBw*.9, comm->nNodes > 1 ? 70.0 : 90.0);
if (a == NCCL_ALGO_TREE && p == NCCL_PROTO_LL) busBw *= 1.0/3.0;
if (a == NCCL_ALGO_TREE && p == NCCL_PROTO_LL128) busBw *= 7.0/9.0;
// Convert bus BW to algorithm BW
float ratio = a == NCCL_ALGO_TREE ? .5 : (1.0 * comm->nRanks) / nsteps;
comm->bandwidths[coll][a][p] = busBw * ratio;
comm->latencies[coll][a][p] = baseLat[a][p];
if (a == NCCL_ALGO_RING) {
float lat = hwLat[hw[a]][a][p];
if ((coll == ncclCollReduce || coll == ncclCollBroadcast)) {
if (ringGraph->sameChannels) {
comm->latencies[coll][a][p] += lat;
} else {
if (p == NCCL_PROTO_SIMPLE) lat = hwLat[hw[a]][NCCL_ALGO_TREE][p]; // Add some chunk latency, waiting for proper chunk modeling
comm->latencies[coll][a][p] += nsteps*lat;
}
} else {
comm->latencies[coll][a][p] += nsteps*lat;
}
} else {
float intraLat = hwLat[intraHw[a]][a][p];
float interLat = hwLat[NCCL_HW_NET][a][p];
comm->latencies[coll][a][p] +=
2 * ((comm->nRanks/comm->nNodes-1) * intraLat + log2i(comm->nNodes) * interLat);
}
}
}
}
// Protocols/Algorithms enable/disable, and user overrides.
// All are enabled except ll128 which is enabled by default only in certain cases.
int protoEnable[NCCL_NUM_PROTOCOLS] = { 1, 2, 1 };
int algoEnable[NCCL_NUM_ALGORITHMS] = { 1, 1 };
const char *protoStr = getenv("NCCL_PROTO");
if (protoStr) NCCLCHECK(parseList(protoStr, ncclProtoStr, NCCL_NUM_PROTOCOLS, protoEnable));
const char *algoStr = getenv("NCCL_ALGO");
if (algoStr) NCCLCHECK(parseList(algoStr, ncclAlgoStr, NCCL_NUM_ALGORITHMS, algoEnable));
for (int c=0; c<NCCL_NUM_FUNCTIONS; c++) for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
int pEnable = protoEnable[p];
if (pEnable == 2 && p == NCCL_PROTO_LL128) {
// Enable LL128 by default only on Volta+NVLink. Other cases are not tested and may cause silent data corruption.
pEnable = (graphs[a]->type <= LINK_PCI) && graphs[a]->nvlink && minCompCap == 70 && maxCompCap == 70 ? 1 : 0;
}
if (pEnable == 0 || algoEnable[a] == 0) comm->bandwidths[c][a][p] = 0;
}
if (comm->rank == 0) {
char line[1024];
int offset = 0;
sprintf(line, "Latency/AlgBw |");
offset = strlen(line);
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
sprintf(line+offset, " %4s/%6s |", ncclAlgoStr[a], ncclProtoStr[p]);
offset = strlen(line);
}
}
INFO(NCCL_TUNING, "%s", line);
for (int c=0; c<NCCL_NUM_FUNCTIONS; c++) {
sprintf(line, "%13s |", ncclFuncStr[c]);
offset = strlen(line);
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
sprintf(line+offset, "%7.1f/%5.1f|", comm->latencies[c][a][p], comm->bandwidths[c][a][p]);
offset = strlen(line);
}
}
INFO(NCCL_TUNING, "%s", line);
}
}
// Set per-thread amount of work before we increase nThreads and nChannels
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
comm->threadThresholds[a][NCCL_PROTO_LL] = NCCL_LL_THREAD_THRESHOLD;
comm->threadThresholds[a][NCCL_PROTO_LL128] = NCCL_LL128_THREAD_THRESHOLD;
comm->threadThresholds[a][NCCL_PROTO_SIMPLE] = NCCL_SIMPLE_THREAD_THRESHOLD;
}
comm->threadThresholds[NCCL_ALGO_RING][NCCL_PROTO_LL] *= comm->nRanks;
// Override defaults with user env
char* str = getenv("NCCL_THREAD_THRESHOLDS");
if (str) {
ssize_t t[NCCL_NUM_ALGORITHMS][NCCL_NUM_PROTOCOLS] = {{ -2, -2, -2 }, { -2, -2, -2}};
sscanf(str, "%ld %ld %ld %ld %ld %ld", t[0], t[0]+1, t[0]+2, t[1], t[1]+1, t[1]+2);
for (int a=0; a<NCCL_NUM_ALGORITHMS; a++) {
for (int p=0; p<NCCL_NUM_PROTOCOLS; p++) {
if (t[a][p] >= 0) comm->threadThresholds[a][p] = t[a][p];
}
}
}
INFO(NCCL_INIT, "threadThresholds %ld/%ld/%ld | %ld/%ld/%ld",
comm->threadThresholds[NCCL_ALGO_TREE][NCCL_PROTO_LL],
comm->threadThresholds[NCCL_ALGO_TREE][NCCL_PROTO_LL128],
comm->threadThresholds[NCCL_ALGO_TREE][NCCL_PROTO_SIMPLE],
comm->threadThresholds[NCCL_ALGO_RING][NCCL_PROTO_LL],
comm->threadThresholds[NCCL_ALGO_RING][NCCL_PROTO_LL128],
comm->threadThresholds[NCCL_ALGO_RING][NCCL_PROTO_SIMPLE]);
return ncclSuccess;
}
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