Re: [PATCH] kernel-shark: Multi-thread the computaion of CPU graph

[Yordan Karadzhov <y.karadz@xxxxxxxxx>]

Hi Libo,

I like the idea of the patch, however a bit of extra work is needed 
before merging it. See my comments in the code below.

On 9/23/24 12:09, Libo Chen wrote:
> Parallelize _newCPUGraph() calls to dramatically speed up
> graph rendering particularly for traces from very large systems.
>
> OpenMP technically is a new dependency here, but it's so embedded
> with GCC toolchains, as long as your GCC is not older than v4.9,
> the libgomp library that comes with it will work.
>
> Signed-off-by: Libo Chen <libo.chen@xxxxxxxxxx>
> ---
>   CMakeLists.txt     |  5 +++++
>   src/KsGLWidget.cpp | 15 ++++++++++++++-
>   2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/CMakeLists.txt b/CMakeLists.txt
> index c36d757..8dd9ff9 100644
> --- a/CMakeLists.txt
> +++ b/CMakeLists.txt
> @@ -84,6 +84,11 @@ set(EXECUTABLE_OUTPUT_PATH "${KS_DIR}/bin")
>   set(CMAKE_C_FLAGS   "${CMAKE_C_FLAGS} -Wall -Wextra -pthread -fPIC -fno-common")
>   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -pthread -fPIC -fno-common")
>   
> +find_package(OpenMP 3.2.5)
> +if (OPENMP_FOUND)
> +    set(CMAKE_C_FLAGS   "${CMAKE_C_FLAGS}   ${OpenMP_C_FLAGS}")
> +    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")

The "if" must be closed.

> +
>   set(CMAKE_CXX_STANDARD 17)
>   set(CMAKE_CXX_STANDARD_REQUIRED ON)
>   set(CMAKE_CXX_EXTENSIONS OFF)
> diff --git a/src/KsGLWidget.cpp b/src/KsGLWidget.cpp
> index 9311d98..00a1951 100644
> --- a/src/KsGLWidget.cpp
> +++ b/src/KsGLWidget.cpp
> @@ -13,6 +13,9 @@
>   #include <GL/glut.h>
>   #include <GL/gl.h>
>   
> +// OpenMP
> +#include <omp.h>
> +
>   // KernelShark
>   #include "libkshark-plugin.h"
>   #include "KsGLWidget.hpp"
> @@ -690,10 +693,20 @@ void KsGLWidget::_makeGraphs()
>   
>   	for (auto it = _streamPlots.begin(); it != _streamPlots.end(); ++it) {
>   		sd = it.key();
> +		QVector<KsPlot::Graph *> cpuGraphs(it.value()._cpuList.count());
> +		QVector<KsPlot::Graph *> taskGraphs(it.value()._taskList.count());
> +
>   		/* Create CPU graphs according to the cpuList. */
>   		it.value()._cpuGraphs = {};
> +		omp_set_num_threads(omp_get_num_procs());

Not sure how setting the thread number works in opm, but I would guess 
that you have to do it just once. If this is the case, please move the 
the line above to the constructor. Note that _makeGraphs() gets executed 
almost every time you do something in the GUI (zoom, shift, select 
event, ...)

> +		#pragma omp parallel for
>   		for (auto const &cpu: it.value()._cpuList) {
> -			g = lamAddGraph(sd, _newCPUGraph(sd, cpu), _vSpacing);
> +			int idx = it.value()._cpuList.indexOf(cpu);
> +			cpuGraphs[idx] = _newCPUGraph(sd, cpu);
> +		}
> +		QVectorIterator<KsPlot::Graph *> itCpuGraphs(cpuGraphs);
> +		while (itCpuGraphs.hasNext()) {
> +			g = lamAddGraph(sd, itCpuGraphs.next(), _vSpacing);
>   			it.value()._cpuGraphs.append(g);
>   		}
>   

I wonder why you add this optimization only for the CPU graphs? Please 
do the same for the Task and Combo graphs as well.

Thanks!
Yordan