Then, you can pass the option --cfg=smpi/shared-malloc-hugepage:/home/huge
to smpirun to actually activate the huge page support in shared mallocs.
-@subsection options_model_smpi_wtime smpi/wtime: Inject constant times for calls to MPI_Wtime
+@subsection options_model_smpi_wtime smpi/wtime: Inject constant times for calls to MPI_Wtime, gettimeofday and clock_gettime
-@b Default value: 0
-
-By setting this option, you can control the amount of time a process sleeps
-when MPI_Wtime() is called; this is important, because SimGrid normally only
-advances the time while communication is happening and thus,
-MPI_Wtime will not add to the time, resulting in a deadlock if used as a
-break-condition.
+@b Default value: 1ms
-Here is an example:
+This option controls the amount of (simulated) time spent in calls to
+MPI_Wtime(), gettimeofday() and clock_gettime(). If you set this value
+to 0, the simulated clock is not advanced in these calls, which leads
+to issue if your application contains such a loop:
@code{.unparsed}
while(MPI_Wtime() < some_time_bound) {
- ...
+ /* some tests, with no communication nor computation */
}
@endcode
-If the time is never advanced, this loop will clearly never end as MPI_Wtime()
-always returns the same value. Hence, pass a (small) value to the smpi/wtime
-option to force a call to MPI_Wtime to advance the time as well.
-
+When the option smpi/wtime is set to 0, the time advances only on
+communications and computations, so the previous code results in an
+infinite loop: the current [simulated] time will never reach @c
+some_time_bound. This infinite loop is avoided when that option is
+set to a small amount, as it is by default since SimGrid v3.21.
+
+Note that if your application does not contain any loop depending on
+the current time only, then setting this option to a non-zero value
+will slow down your simulations by a tiny bit: the simulation loop has
+to be broken and reset each time your code ask for the current time.
+If the simulation speed really matters to you, you can avoid this
+extra delay by setting smpi/wtime to 0.
@section options_generic Configuring other aspects of SimGrid
XBT_LOG_NEW_DEFAULT_SUBCATEGORY(smpi_bench, smpi, "Logging specific to SMPI (benchmarking)");
-static simgrid::config::Flag<double> smpi_wtime_sleep("smpi/wtime", "Minimum time to inject inside a call to MPI_Wtime",
- 0.0);
+static simgrid::config::Flag<double>
+ smpi_wtime_sleep("smpi/wtime",
+ "Minimum time to inject inside a call to MPI_Wtime(), gettimeofday() and clock_gettime()",
+ 1e-6 /* Documented to be 1ms */);
double smpi_cpu_threshold = -1;
double smpi_host_speed;
tv->tv_usec = static_cast<suseconds_t>((now - tv->tv_sec) * 1e6);
#endif
}
+ if (smpi_wtime_sleep > 0)
+ simcall_process_sleep(smpi_wtime_sleep);
smpi_bench_begin();
return 0;
}
tp->tv_sec = static_cast<time_t>(now);
tp->tv_nsec = static_cast<long int>((now - tp->tv_sec) * 1e9);
}
+ if (smpi_wtime_sleep > 0)
+ simcall_process_sleep(smpi_wtime_sleep);
smpi_bench_begin();
return 0;
}
#endif
+double smpi_mpi_wtime()
+{
+ double time;
+ if (smpi_process()->initialized() && not smpi_process()->finalized() && not smpi_process()->sampling()) {
+ smpi_bench_end();
+ time = SIMIX_get_clock();
+ if (smpi_wtime_sleep > 0)
+ simcall_process_sleep(smpi_wtime_sleep);
+ smpi_bench_begin();
+ } else {
+ time = SIMIX_get_clock();
+ }
+ return time;
+}
+
extern double sg_surf_precision;
unsigned long long smpi_rastro_resolution ()
{
return static_cast<unsigned long long>(sec) * smpi_rastro_resolution() + pre;
}
-double smpi_mpi_wtime()
-{
- double time;
- if (smpi_process()->initialized() && not smpi_process()->finalized() && not smpi_process()->sampling()) {
- smpi_bench_end();
- time = SIMIX_get_clock();
- // to avoid deadlocks if used as a break condition, such as
- // while (MPI_Wtime(...) < time_limit) {
- // ....
- // }
- // because the time will not normally advance when only calls to MPI_Wtime
- // are made -> deadlock (MPI_Wtime never reaches the time limit)
- if (smpi_wtime_sleep > 0)
- simcall_process_sleep(smpi_wtime_sleep);
- smpi_bench_begin();
- } else {
- time = SIMIX_get_clock();
- }
- return time;
-}
-
/* ****************************** Functions related to the SMPI_SAMPLE_ macros ************************************/
namespace {
class SampleLocation : public std::string {