time measuring tweaks.

C-optimized/README.md

@@ -7,13 +7,18 @@ The main changes are:
 - an optimization of the mixture function (it passes the functions instead of the whole arrays, reducing in great measure the memory usage and the computation time) and 
 - the implementation of multi-threading with OpenMP. 
 
+## Performance
+
 The mean time of execution is 6 ms. With the following distribution:
 
 ![Time histogram](https://i.imgur.com/6iT2PkF.png)
 
 The hardware used has been an AMD 5800x3D and 16GB of DDR4-3200 MHz.
 
-Take into account that the multi-threading introduces a bit of dispersion in the execution time due to the creation and destruction of threads. 
-
 Also, the time data has been collected by executing the interior of the main() function 1000 times in a for loop, not executing the program itself 1000 times.
 
+## Multithreading
+
+Take into account that the multi-threading introduces a bit of dispersion in the execution time due to the creation and destruction of threads. 
+
+In Nuño's machine, multithreading actually introduces a noticeable slowdown factor.

C-optimized/makefile

@@ -37,27 +37,17 @@ format: $(SRC)
 	$(FORMATTER) $(SRC)
 
 run: $(SRC) $(OUTPUT)
-	OMP_NUM_THREADS=4 ./$(OUTPUT)
-
-test: $(SRC) $(OUTPUT)
 	OMP_NUM_THREADS=1 ./$(OUTPUT)
-	echo ""
-	OMP_NUM_THREADS=2 ./$(OUTPUT)
-	echo ""
+
+multi: $(SRC) $(OUTPUT)
+	OMP_NUM_THREADS=1 ./$(OUTPUT) && echo
+	OMP_NUM_THREADS=2 ./$(OUTPUT) && echo
 	OMP_NUM_THREADS=4 ./$(OUTPUT)
 
-#	echo "Increasing stack size limit, because we are dealing with 1M samples"
-#	# ulimit: increase stack size limit
-#	# -Ss: the soft limit. If you set the hard limit, you then can't raise it
-#	# 256000: around 250Mbs, if I'm reading it correctly.
-#	# Then run the program
-#	ulimit -Ss 256000 && ./$(OUTPUT)
+time:
+	OMP_NUM_THREADS=1 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+	OMP_NUM_THREADS=2 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
+	OMP_NUM_THREADS=4 /bin/time -f "Time: %es" ./$(OUTPUT) && echo
 
 linux-install:
 	sudo apt-get install libomp-dev
-
-# Old:
-# Link libraries, for good measure
-# LD_LIBRARY_PATH=/usr/local/lib
-# export LD_LIBRARY_PATH
-

C-optimized/samples.c

@@ -245,8 +245,8 @@ int main()
     //initialize randomness
     srand(time(NULL));
     
-		clock_t start, end;
-		start = clock();
+		// clock_t start, end;
+		// start = clock();
 
 		// Toy example
 		// Declare variables in play
@@ -269,10 +269,14 @@ int main()
 
 		mixture_f(samplers, weights, n_dists, dist_mixture, n_threads);
 		printf("Sum(dist_mixture, N)/N = %f\n", split_array_sum(dist_mixture, N, n_threads) / N);
-
+		// array_print(dist_mixture[0], N);
 		split_array_free(dist_mixture, n_threads);
 		
-		end = clock();
-		printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC * 10) * 1000);
+		// end = clock();
+		// printf("Time (ms): %f\n", ((double)(end - start)) / (CLOCKS_PER_SEC * 10) * 1000);
+		// ^ Will only measure how long it takes the inner main to run, not the whole program, 
+		// including e.g., loading the program into memory or smth.
+		// Also CLOCKS_PER_SEC in POSIX is a constant equal to 1000000.
+		// See: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
     return 0;
 }

C/samples.c

@@ -3,6 +3,7 @@
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <time.h>
 
 #define N 1000000
 /* 
@@ -111,6 +112,10 @@ void mixture(gsl_rng* r, double* dists[], double* weights, int n, double* result
 /* Main */
 int main(void)
 {
+		// Start clock
+    clock_t start, end;
+    start = clock();
+
     /* Initialize GNU Statistical Library (GSL) stuff */
     const gsl_rng_type* T;
     gsl_rng* r;
@@ -144,6 +149,9 @@ int main(void)
     /* Clean up GSL */
     gsl_rng_free(r);
 		
+		// End clock
+    end = clock();
+    printf("Total time (ms): %f\n", ((double)(end - start)) / CLOCKS_PER_SEC * 1000);
     /* Return success*/
     return EXIT_SUCCESS;
 }

README.md

@@ -30,13 +30,14 @@ As of now, it may be useful for checking the validity of simple estimations. The
 ## Comparison table
 
 | Language                 | Time      | Lines of code |
-|----------------------|-----------|---------------|
-| Nim                  | 0m0.068s  | 84  |
-| C                    | 0m0.292s  | 149 |
-| Javascript (NodeJS)  | 0m0,732s  | 69  |
-| Squiggle             | 0m1,536s  | 14  |
-| R                    | 0m7,000s  | 49  |
-| Python (CPython)     | 0m16,641s | 56  |
+|--------------------------|-----------|---------------|
+| C (optimized, 1 thread)  | ~30ms     | 282 |
+| Nim                      | 68ms      | 84  |
+| C                        | 292ms     | 149 |
+| Javascript (NodeJS)      | 732ms     | 69  |
+| Squiggle                 | 1,536s    | 14  |
+| R                        | 7,000s    | 49  |
+| Python (CPython)         | 16,641s   | 56  |
 
 Time measurements taken with the [time](https://man7.org/linux/man-pages/man1/time.1.html) tool, using 1M samples:
 
@@ -51,7 +52,9 @@ I was really happy trying [Nim](https://nim-lang.org/), and as a result the Nim
 
 Without 1. and 2., the nim code takes 0m0.183s instead. But I don't think that these are unfair advantages: I liked trying out nim and therefore put in more love into the code, and this seems like it could be a recurring factor.
 
-For C, I enabled the `-Ofast` compilation flag. Without it, it instead takes ~0.4 seconds. Initially, before I enabled the `-Ofast` flag, I was surprised that the Node and Squiggle code were comparable to the C code. Using [bun](https://bun.sh/) instead of node is actually a bit slower.
+For the initial C code, I enabled the `-Ofast` compilation flag. Without it, it instead takes ~0.4 seconds. Initially, before I enabled the `-Ofast` flag, I was surprised that the Node and Squiggle code were comparable to the C code. Using [bun](https://bun.sh/) instead of node is actually a bit slower.
+
+For the optimized C code, see [that folder's README](./C-optimized/README.md).
 
 For the Python code, it's possible that the lack of speed is more a function of me not being as familiar with Python. It's also very possible that the code would run faster with [PyPy](https://doc.pypy.org).
 

time.txt

@@ -1,3 +1,17 @@
+# Optimized C
+
+OMP_NUM_THREADS=1 /bin/time -f "Time: %es" ./out/samples && echo
+Sum(dist_mixture, N)/N = 0.885837
+Time: 0.02s
+
+OMP_NUM_THREADS=2 /bin/time -f "Time: %es" ./out/samples && echo
+Sum(dist_mixture, N)/N = 0.885123
+Time: 0.14s
+
+OMP_NUM_THREADS=4 /bin/time -f "Time: %es" ./out/samples && echo
+Sum(dist_mixture, N)/N = 0.886255
+Time: 0.11s
+
 # C
 
 ## normal compilation