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Reference documentation for deal.II version 9.1.0-pre
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Reference documentation for deal.II version 9.1.0-pre
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#include <deal.II/base/timer.h>
Classes | |
| class | Scope |
| struct | Section |
Public Types |
Public Member Functions | |
| TimerOutput (std::ostream &stream, const OutputFrequency output_frequency, const OutputType output_type) | |
| TimerOutput (ConditionalOStream &stream, const OutputFrequency output_frequency, const OutputType output_type) | |
| TimerOutput (MPI_Comm mpi_comm, std::ostream &stream, const OutputFrequency output_frequency, const OutputType output_type) | |
| TimerOutput (MPI_Comm mpi_comm, ConditionalOStream &stream, const OutputFrequency output_frequency, const OutputType output_type) | |
| ~TimerOutput () | |
| void | enter_subsection (const std::string §ion_name) |
| void | enter_section (const std::string §ion_name) |
| void | leave_subsection (const std::string §ion_name=std::string()) |
| void | exit_section (const std::string §ion_name=std::string()) |
| std::map< std::string, double > | get_summary_data (const OutputData kind) const |
| void | print_summary () const |
| void | disable_output () |
| void | enable_output () |
| void | reset () |
Private Attributes | |
| OutputFrequency | output_frequency |
| OutputType | output_type |
| Timer | timer_all |
| std::map< std::string, Section > | sections |
| ConditionalOStream | out_stream |
| bool | output_is_enabled |
| std::list< std::string > | active_sections |
| MPI_Comm | mpi_communicator |
| Threads::Mutex | mutex |
This class can be used to generate formatted output from time measurements of different subsections in a program. It is possible to create several sections that perform certain aspects of the program. A section can be entered several times. By changing the options in OutputFrequency and OutputType, the user can choose whether output should be generated every time a section is joined or just in the end of the program. Moreover, it is possible to show CPU times, wall times or both.
Use of this class could be as follows:
When run, this program will return an output like this:
The output will see that we entered the assembly and solve section twice, and reports how much time we spent there. Moreover, the class measures the total time spent from start to termination of the TimerOutput object. In this case, we did a lot of other stuff, so that the time proportions of the functions we measured are far away from 100 percent.
The scheme above where you have to have calls to TimerOutput::enter_subsection() and TimerOutput::leave_subsection() is awkward if the sections in between these calls contain return statements or may throw exceptions. In that case, it is easy to forget that one nevertheless needs to leave the section somehow, somewhere. An easier approach is to use "scoped" sections. This is a variable that when you create it enters a section, and leaves the section when you destroy it. If this is a variable local to a particular scope (a code block between curly braces) and you leave this scope due to a return statements or an exception, then the variable is destroyed and the timed section is left automatically. Consequently, we could have written the code piece above as follows, with exactly the same result but now exception-safe:
In a parallel program built on MPI, using the class in a way such as the one shown above would result in a situation where each process times the corresponding sections and then outputs the resulting timing information at the end. This is annoying since you'd get a lot of output – one set of timing information from each processor.
This can be avoided by only letting one processor generate screen output, typically by using an object of type ConditionalOStream instead of std::cout to write to screen (see, for example, step-17, step-18, step-32 and step-40, all of which use this method).
This way, only a single processor outputs timing information, typically the first process in the MPI universe. However, if you take the above code snippet as an example, imagine what would happen if setup_dofs() is fast on processor zero and slow on at least one of the other processors; and if the first thing assemble_system_1() does is something that requires all processors to communicate. In this case, on processor zero, the timing section with name "Setup dof system" will yield a short run time on processor zero, whereas the section "Assemble" will take a long time: not because assemble_system_1() takes a particularly long time, but because on the processor on which we time (or, rather, the one on which we generate output) happens to have to wait for a long time till the other processor is finally done with setup_dofs() and starts to participate in assemble_system_1(). In other words, the timing that is reported is unreliable because it reflects run times from other processors. Furthermore, the run time of this section on processor zero has nothing to do with the run time of the section on other processors but instead with the run time of the previous section on another processor.
The usual way to avoid this is to introduce a barrier into the parallel code just before we start and stop timing sections. This ensures that all processes are at the same place and the timing information then reflects the maximal run time across all processors. To achieve this, you need to initialize the TimerOutput object with an MPI communicator object, for example as in the following code:
Here, pcout is an object of type ConditionalOStream that makes sure that we only generate output on a single processor. See the step-32, step-40, and step-42 tutorial programs for this kind of usage of this class.
An enumeration data type that describes whether to generate output every time we exit a section, just in the end, both, or never.
An enumeration data type that describes whether to show CPU times, wall times, or both CPU and wall times whenever we generate output.
| TimerOutput::TimerOutput | ( | std::ostream & | stream, |
| const OutputFrequency | output_frequency, | ||
| const OutputType | output_type | ||
| ) |
Constructor.
| stream | The stream (of type std::ostream) to which output is written. |
| output_frequency | A variable indicating when output is to be written to the given stream. |
| output_type | A variable indicating what kind of timing the output should represent (CPU or wall time). |
| TimerOutput::TimerOutput | ( | ConditionalOStream & | stream, |
| const OutputFrequency | output_frequency, | ||
| const OutputType | output_type | ||
| ) |
Constructor.
| stream | The stream (of type ConditionalOstream) to which output is written. |
| output_frequency | A variable indicating when output is to be written to the given stream. |
| output_type | A variable indicating what kind of timing the output should represent (CPU or wall time). |
| TimerOutput::TimerOutput | ( | MPI_Comm | mpi_comm, |
| std::ostream & | stream, | ||
| const OutputFrequency | output_frequency, | ||
| const OutputType | output_type | ||
| ) |
Constructor that takes an MPI communicator as input. A timer constructed this way will sum up the CPU times over all processors in the MPI network for calculating the CPU time, or take the maximum over all processors, depending on the value of output_type . See the documentation of this class for the rationale for this constructor and an example.
| mpi_comm | An MPI communicator across which we should accumulate or otherwise synchronize the timing information we produce on every MPI process. |
| stream | The stream (of type std::ostream) to which output is written. |
| output_frequency | A variable indicating when output is to be written to the given stream. |
| output_type | A variable indicating what kind of timing the output should represent (CPU or wall time). In this parallel context, when this argument selects CPU time, then times are accumulated over all processes participating in the MPI communicator. If this argument selects wall time, then reported times are the maximum over all processors' run times for this section. (The latter is computed by placing an MPI_Barrier call before starting and stopping the timer for each section. |
| TimerOutput::TimerOutput | ( | MPI_Comm | mpi_comm, |
| ConditionalOStream & | stream, | ||
| const OutputFrequency | output_frequency, | ||
| const OutputType | output_type | ||
| ) |
Constructor that takes an MPI communicator as input. A timer constructed this way will sum up the CPU times over all processors in the MPI network for calculating the CPU time, or take the maximum over all processors, depending on the value of output_type . See the documentation of this class for the rationale for this constructor and an example.
| mpi_comm | An MPI communicator across which we should accumulate or otherwise synchronize the timing information we produce on every MPI process. |
| stream | The stream (of type ConditionalOstream) to which output is written. |
| output_frequency | A variable indicating when output is to be written to the given stream. |
| output_type | A variable indicating what kind of timing the output should represent (CPU or wall time). In this parallel context, when this argument selects CPU time, then times are accumulated over all processes participating in the MPI communicator. If this argument selects wall time, then reported times are the maximum over all processors' run times for this section. (The latter is computed by placing an MPI_Barrier call before starting and stopping the timer for each section.) |
| TimerOutput::~TimerOutput | ( | ) |
Destructor. Calls print_summary() in case the option for writing the summary output is set.
| void TimerOutput::enter_subsection | ( | const std::string & | section_name | ) |
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| void TimerOutput::leave_subsection | ( | const std::string & | section_name = std::string() | ) |
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| std::map< std::string, double > TimerOutput::get_summary_data | ( | const OutputData | kind | ) | const |
| void TimerOutput::print_summary | ( | ) | const |
| void TimerOutput::disable_output | ( | ) |
By calling this function, all output can be disabled. This function together with enable_output() can be useful if one wants to control the output in a flexible way without putting a lot of if clauses in the program.
| void TimerOutput::enable_output | ( | ) |
This function re-enables output of this class if it was previously disabled with disable_output(). This function together with disable_output() can be useful if one wants to control the output in a flexible way without putting a lot of if clauses in the program.
| void TimerOutput::reset | ( | ) |
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A list of the sections that have been entered and not exited. The list is kept in the order in which sections have been entered, but elements may be removed in the middle if an argument is given to the exit_section() function.
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1.8.11
