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39 #include "gmx_omp_nthreads.h"
47 #include "gromacs/gmxlib/network.h"
48 #include "gromacs/mdtypes/commrec.h"
49 #include "gromacs/utility/cstringutil.h"
50 #include "gromacs/utility/enumerationhelpers.h"
51 #include "gromacs/utility/fatalerror.h"
52 #include "gromacs/utility/gmxassert.h"
53 #include "gromacs/utility/gmxomp.h"
54 #include "gromacs/utility/logger.h"
55 #include "gromacs/utility/programcontext.h"
57 /** Structure with the number of threads for each OpenMP multi-threaded
58 * algorithmic module in mdrun. */
61 int gnth; /**< Global num. of threads per PP or PP+PME process/tMPI thread. */
62 int gnth_pme; /**< Global num. of threads per PME only process/tMPI thread. */
64 gmx::EnumerationArray<ModuleMultiThread, int> nth; /**< Number of threads for each module, indexed with module_nth_t */
65 } omp_module_nthreads_t;
67 /** Names of environment variables to set the per module number of threads.
69 * Indexed with the values of module_nth_t.
71 static const char* enumValueToEnvVariableString(ModuleMultiThread enumValue)
73 constexpr gmx::EnumerationArray<ModuleMultiThread, const char*> moduleMultiThreadEnvVariableNames = {
74 "GMX_DEFAULT_NUM_THREADS should never be set",
75 "GMX_DOMDEC_NUM_THREADS",
76 "GMX_PAIRSEARCH_NUM_THREADS",
77 "GMX_NONBONDED_NUM_THREADS",
78 "GMX_LISTED_FORCES_NUM_THREADS",
79 "GMX_PME_NUM_THREADS",
80 "GMX_UPDATE_NUM_THREADS",
81 "GMX_VSITE_NUM_THREADS",
82 "GMX_LINCS_NUM_THREADS",
83 "GMX_SETTLE_NUM_THREADS"
85 return moduleMultiThreadEnvVariableNames[enumValue];
88 /** Names of the modules. */
89 static const char* enumValueToString(ModuleMultiThread enumValue)
91 constexpr gmx::EnumerationArray<ModuleMultiThread, const char*> moduleMultiThreadNames = {
92 "default", "domain decomposition",
93 "pair search", "non-bonded",
98 return moduleMultiThreadNames[enumValue];
101 /** Number of threads for each algorithmic module.
103 * File-scope global variable that gets set once in pick_module_nthreads()
104 * and queried via gmx_omp_nthreads_get().
106 * All fields are initialized to 0 which should result in errors if
107 * the init call is omitted.
109 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
110 static omp_module_nthreads_t modth = { 0, 0, { 0, 0, 0, 0, 0, 0, 0, 0, 0 } };
113 /** Determine the number of threads for module \p mod.
115 * \p m takes values form the module_nth_t enum and maps these to the
116 * corresponding value in modth_env_var.
118 * Each number of threads per module takes the default value unless
119 * GMX_*_NUM_THERADS env var is set, case in which its value overrides
122 static void pick_module_nthreads(const gmx::MDLogger& mdlog, ModuleMultiThread m, gmx_bool bSepPME)
127 const bool bOMP = GMX_OPENMP;
129 /* The default should never be set through a GMX_*_NUM_THREADS env var
130 * as it's always equal with gnth. */
131 if (m == ModuleMultiThread::Default)
136 /* check the environment variable */
137 if ((env = getenv(enumValueToEnvVariableString(m))) != nullptr)
139 sscanf(env, "%d", &nth);
143 gmx_warning("%s=%d is set, but %s is compiled without OpenMP!",
144 enumValueToEnvVariableString(m),
146 gmx::getProgramContext().displayName());
149 /* with the verlet codepath, when any GMX_*_NUM_THREADS env var is set,
150 * OMP_NUM_THREADS also has to be set */
151 if (getenv("OMP_NUM_THREADS") == nullptr)
154 "%s=%d is set, the default number of threads also "
155 "needs to be set with OMP_NUM_THREADS!",
156 enumValueToEnvVariableString(m),
160 /* only babble if we are really overriding with a different value */
161 if ((bSepPME && m == ModuleMultiThread::Pme && nth != modth.gnth_pme) || (nth != modth.gnth))
163 GMX_LOG(mdlog.warning)
165 .appendTextFormatted("%s=%d set, overriding the default number of %s threads",
166 enumValueToString(m),
168 enumValueToEnvVariableString(m));
173 /* pick the global PME node nthreads if we are setting the number
174 * of threads in separate PME nodes */
175 nth = (bSepPME && m == ModuleMultiThread::Pme) ? modth.gnth_pme : modth.gnth;
178 gmx_omp_nthreads_set(m, nth);
181 void gmx_omp_nthreads_read_env(const gmx::MDLogger& mdlog, int* nthreads_omp)
184 gmx_bool bCommandLineSetNthreadsOMP = *nthreads_omp > 0;
187 GMX_RELEASE_ASSERT(nthreads_omp, "nthreads_omp must be a non-NULL pointer");
189 if ((env = getenv("OMP_NUM_THREADS")) != nullptr)
193 sscanf(env, "%d", &nt_omp);
196 gmx_fatal(FARGS, "OMP_NUM_THREADS is invalid: '%s'", env);
199 if (bCommandLineSetNthreadsOMP && nt_omp != *nthreads_omp)
202 "Environment variable OMP_NUM_THREADS (%d) and the number of threads "
203 "requested on the command line (%d) have different values. Either omit one, "
204 "or set them both to the same value.",
209 /* Setting the number of OpenMP threads. */
210 *nthreads_omp = nt_omp;
212 /* Output the results */
214 "\nThe number of OpenMP threads was set by environment variable OMP_NUM_THREADS to "
217 bCommandLineSetNthreadsOMP ? " (and the command-line setting agreed with that)" : "");
219 /* This prints once per simulation for multi-simulations,
220 * which might help diagnose issues with inhomogenous
222 GMX_LOG(mdlog.info).appendTextFormatted("%s", buffer);
225 /* This prints once per process for real MPI (i.e. once
226 * per debug file), and once per simulation for thread MPI
227 * (because of logic in the calling function). */
228 fputs(buffer, debug);
233 /*! \brief Helper function for parsing various input about the number
234 of OpenMP threads to use in various modules and deciding what to
236 static void manage_number_of_openmp_threads(const gmx::MDLogger& mdlog,
239 int nthreads_hw_avail,
240 int omp_nthreads_req,
241 int omp_nthreads_pme_req,
242 gmx_bool gmx_unused bThisNodePMEOnly,
243 int numRanksOnThisNode,
250 /* modth is shared among tMPI threads, so for thread safety, the
251 * detection is done on the master only. It is not thread-safe
252 * with multiple simulations, but that's anyway not supported by
259 GMX_UNUSED_VALUE(cr);
262 /* With full OpenMP support (verlet scheme) set the number of threads
263 * per process / default:
264 * - 1 if not compiled with OpenMP or
265 * - OMP_NUM_THREADS if the env. var is set, or
266 * - omp_nthreads_req = #of threads requested by the user on the mdrun
267 * command line, otherwise
268 * - take the max number of available threads and distribute them
269 * on the processes/tMPI threads.
270 * ~ The GMX_*_NUM_THREADS env var overrides the number of threads of
271 * the respective module and it has to be used in conjunction with
274 * The number of PME threads is equal to:
275 * - 1 if not compiled with OpenMP or
276 * - GMX_PME_NUM_THREADS if defined, otherwise
277 * - OMP_NUM_THREADS if defined, otherwise
281 if ((env = getenv("OMP_NUM_THREADS")) != nullptr)
283 if (!bOMP && (std::strncmp(env, "1", 1) != 0))
285 gmx_warning("OMP_NUM_THREADS is set, but %s was compiled without OpenMP support!",
286 gmx::getProgramContext().displayName());
290 nth = gmx_omp_get_max_threads();
293 else if (omp_nthreads_req > 0)
295 nth = omp_nthreads_req;
299 /* max available threads per node */
300 nth = nthreads_hw_avail;
302 /* divide the threads among the MPI ranks */
303 if (nth >= numRanksOnThisNode)
305 nth /= numRanksOnThisNode;
313 /* now we have the global values, set them:
314 * - 1 if not compiled with OpenMP
315 * - nth for the verlet scheme when compiled with OpenMP
328 if (omp_nthreads_pme_req > 0)
330 modth.gnth_pme = omp_nthreads_pme_req;
334 modth.gnth_pme = nth;
342 /* now set the per-module values */
343 modth.nth[ModuleMultiThread::Default] = modth.gnth;
344 pick_module_nthreads(mdlog, ModuleMultiThread::Domdec, bSepPME);
345 pick_module_nthreads(mdlog, ModuleMultiThread::Pairsearch, bSepPME);
346 pick_module_nthreads(mdlog, ModuleMultiThread::Nonbonded, bSepPME);
347 pick_module_nthreads(mdlog, ModuleMultiThread::Bonded, bSepPME);
348 pick_module_nthreads(mdlog, ModuleMultiThread::Pme, bSepPME);
349 pick_module_nthreads(mdlog, ModuleMultiThread::Update, bSepPME);
350 pick_module_nthreads(mdlog, ModuleMultiThread::VirtualSite, bSepPME);
351 pick_module_nthreads(mdlog, ModuleMultiThread::Lincs, bSepPME);
352 pick_module_nthreads(mdlog, ModuleMultiThread::Settle, bSepPME);
354 /* set the number of threads globally */
358 if (bThisNodePMEOnly)
360 gmx_omp_set_num_threads(modth.gnth_pme);
363 #endif /* GMX_THREAD_MPI */
365 gmx_omp_set_num_threads(nth);
370 /*! \brief Report on the OpenMP settings that will be used */
371 static void reportOpenmpSettings(const gmx::MDLogger& mdlog, const t_commrec* cr, gmx_bool bOMP, gmx_bool bSepPME)
374 const char* mpi_str = "per tMPI thread";
376 const char* mpi_str = "per MPI process";
378 int nth_min, nth_max, nth_pme_min, nth_pme_max;
380 /* inform the user about the settings */
389 /* Get the min and max thread counts over the MPI ranks */
390 int buf_in[4], buf_out[4];
392 buf_in[0] = -modth.gnth;
393 buf_in[1] = modth.gnth;
394 buf_in[2] = -modth.gnth_pme;
395 buf_in[3] = modth.gnth_pme;
397 MPI_Allreduce(buf_in, buf_out, 4, MPI_INT, MPI_MAX, cr->mpi_comm_mysim);
399 nth_min = -buf_out[0];
400 nth_max = buf_out[1];
401 nth_pme_min = -buf_out[2];
402 nth_pme_max = buf_out[3];
407 nth_min = modth.gnth;
408 nth_max = modth.gnth;
409 nth_pme_min = modth.gnth_pme;
410 nth_pme_max = modth.gnth_pme;
414 if (nth_max == nth_min)
416 GMX_LOG(mdlog.warning)
417 .appendTextFormatted("Using %d OpenMP thread%s %s",
419 nth_min > 1 ? "s" : "",
420 cr->nnodes > 1 ? mpi_str : "");
424 GMX_LOG(mdlog.warning).appendTextFormatted("Using %d - %d OpenMP threads %s", nth_min, nth_max, mpi_str);
427 if (bSepPME && (nth_pme_min != nth_min || nth_pme_max != nth_max))
429 if (nth_pme_max == nth_pme_min)
431 GMX_LOG(mdlog.warning)
432 .appendTextFormatted("Using %d OpenMP thread%s %s for PME",
434 nth_pme_min > 1 ? "s" : "",
435 cr->nnodes > 1 ? mpi_str : "");
439 GMX_LOG(mdlog.warning)
440 .appendTextFormatted(
441 "Using %d - %d OpenMP threads %s for PME", nth_pme_min, nth_pme_max, mpi_str);
444 GMX_LOG(mdlog.warning);
447 void gmx_omp_nthreads_init(const gmx::MDLogger& mdlog,
449 int nthreads_hw_avail,
450 int numRanksOnThisNode,
451 int omp_nthreads_req,
452 int omp_nthreads_pme_req,
453 gmx_bool bThisNodePMEOnly)
457 const bool bOMP = GMX_OPENMP;
459 bSepPME = (thisRankHasDuty(cr, DUTY_PP) != thisRankHasDuty(cr, DUTY_PME));
461 manage_number_of_openmp_threads(mdlog,
466 omp_nthreads_pme_req,
471 /* Non-master threads have to wait for the OpenMP management to be
472 * done, so that code elsewhere that uses OpenMP can be certain
473 * the setup is complete. */
476 MPI_Barrier(cr->mpi_comm_mysim);
480 reportOpenmpSettings(mdlog, cr, bOMP, bSepPME);
483 int gmx_omp_nthreads_get(ModuleMultiThread mod)
485 if (mod < ModuleMultiThread::Default || mod >= ModuleMultiThread::Count)
487 /* invalid module queried */
492 return modth.nth[mod];
496 void gmx_omp_nthreads_set(ModuleMultiThread mod, int nthreads)
498 /* Catch an attempt to set the number of threads on an invalid
500 GMX_RELEASE_ASSERT(mod >= ModuleMultiThread::Default && mod < ModuleMultiThread::Count,
501 "Trying to set nthreads on invalid OpenMP module");
503 modth.nth[mod] = nthreads;