From 4650ec4d58e7e153e688b71cd3f20a7be0bbe9d4 Mon Sep 17 00:00:00 2001 From: Xin Li <lxin@kth.se> Date: Fri, 24 Aug 2018 11:01:21 +0200 Subject: [PATCH] updated intro_lab instruction --- intro_lab/README.md | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-) diff --git a/intro_lab/README.md b/intro_lab/README.md index a05ec72..e526020 100644 --- a/intro_lab/README.md +++ b/intro_lab/README.md @@ -55,10 +55,10 @@ export OMP_NUM_THREADS=<number-of-threads> To run an OpenMP code on a computing node of Beskow: ``` -aprun -n 1 -d number of threads -cc none ./name_exec +aprun -n 1 -d <number-of-threads> -cc none ./name_exec ``` -## Exercise-1 - OpenMP Hello World: get familiar with OpenMp Environment +## Exercise 1 - OpenMP Hello World: get familiar with OpenMp Environment _Concepts: Parallel regions, parallel, thread ID_ @@ -98,14 +98,14 @@ Questions: - How many different ways are there to change the number of threads? Which one are those? - How can you make the output ordered from thread 0 to thread 4? -## Exercise 2 - Creating Threads: calculate pi in parallel opnalryaulslienlg tphreagma +## Exercise 2 - Creating Threads: calculate π in parallel using only pragma omp parallel _Concepts: Parallel, default data environment, runtime library calls_ Here we are going to implement a first parallel version of the pi.c / pi.f90 -code to calculate the value of pi using the parallel construct. +code to calculate the value of π using the parallel construct. -The figure below shows the numerical technique, we are going to use to calculate pi. +The figure below shows the numerical technique, we are going to use to calculate π. <img src="image/pi_int.png" alt="PI_integral" width="350px"/> @@ -119,7 +119,7 @@ We can approximate the integral as a sum of rectangles where each rectangle has width Δx and height F(x<sub>i</sub>) at the middle of interval i. -A simple serial C code to calculate pi is the following: +A simple serial C code to calculate π is the following: ``` static long num_steps = 100000000; @@ -192,12 +192,12 @@ Questions: - Is there any technique you heard in class to improve the scalability of the technique? How would you implement it? -## Exercise 3 - calculate picursintgical andatomic directives +## Exercise 3 - Calculate π using critical and atomic directives _Concepts: parallel region, synchronization, critical, atomic_ Here we are going to implement a second and a third parallel version of the -pi.c / pi.f90 code to calculate the value of pi using the critical and atomic +pi.c / pi.f90 code to calculate the value of π using the critical and atomic directives. Instructions: Create two new parallel versions of the pi.c / pi.f90 program @@ -207,7 +207,7 @@ time with 1, 2, 4, 8, 16, 32 threads. Record the timing in a table. Hints: -- We can use a shared variable pi to be updated concurrently by different +- We can use a shared variable π to be updated concurrently by different threads. However, this variable needs to be protected with a critical section or an atomic access. - Use critical and atomic before the update ``pi += step`` @@ -220,12 +220,12 @@ Questions: - Do the two version of the codes differ in performance? If so, what do you think it is the reason? -## Exercise 4 - calculate pi with a loop and a reduction +## Exercise 4 - Calculate π with a loop and a reduction _Concepts: worksharing, parallel loop, schedule, reduction_ Here we are going to implement a fourth parallel version of the pi.c / pi.f90 -code to calculate the value of pi using omp for and reduction operations. +code to calculate the value of π using omp for and reduction operations. Instructions: Create a new parallel versions of the pi.c / pi.f90 program using the parallel construct ``#pragma omp for`` and ``reduction`` operation. Run the new -- GitLab