nbench: Eliminate timing and re-running related code

[MatzeB]

Summary

nbench is by far the noisiest benchmark in the test-suite for me. This
seems to be caused by the benchmark running a variable number of
iterations internally based on its own time measurements. Even though the
original commit to the test-suite claims this was disabled.

This commit shortcuts all the re-running logic and removes
all time measurement code just to be sure.

[kristof.beyls]

I also see nbench consistently being noisy.
The benchmarks in the test-suite should on every run do the same amount of work when invoked in the same way, so indeed, it's broken that nbench changes the number of iterations it runs the way it does at the moment. If such functionality would be needed, it would need to be moved to the test-suite driver level, not be implemented in individual programs.

That being said, while we're fiddling with the number of iterations this benchmark runs, could we reduce this by a factor of about 100, so it runs in between 0.1 and 1 seconds on most systems?
I've started doing analysis on what would be needed to make the test-suite in benchmark mode run an order of magnitude more quickly, so that with the same amount of experimentation time, we could get an order of magnitude more samples to do statistical analysis.
My initial experiments on x86_64 and AArch64 systems indicate that as long as a benchmark runs for at least 0.1 seconds, noise isn't larger than if it runs for much longer.
Making all programs in the test-suite run between 0.1 and 1 second would make the test-suite run probably between 1 and 2 orders of magnitude faster.
In these experiments, I see nbench taking between 0.5% and 3% of the total test-suite running time. So if it's little work to reduce the number of iterations in nbench as part of this work, we at least already have this test-suite speedup in the bank.

Thanks!

Kristof

MultiSource/Benchmarks/nbench/nbench0.c

68

It seems this iter variable is unused, as you declare another iter variable in for-loop-scope below?

[cmatthews]

LGTM.

[MatzeB]

In D21590#464282, @kristof.beyls wrote:

I also see nbench consistently being noisy.
The benchmarks in the test-suite should on every run do the same amount of work when invoked in the same way, so indeed, it's broken that nbench changes the number of iterations it runs the way it does at the moment. If such functionality would be needed, it would need to be moved to the test-suite driver level, not be implemented in individual programs.

That being said, while we're fiddling with the number of iterations this benchmark runs, could we reduce this by a factor of about 100, so it runs in between 0.1 and 1 seconds on most systems?
I've started doing analysis on what would be needed to make the test-suite in benchmark mode run an order of magnitude more quickly, so that with the same amount of experimentation time, we could get an order of magnitude more samples to do statistical analysis.
My initial experiments on x86_64 and AArch64 systems indicate that as long as a benchmark runs for at least 0.1 seconds, noise isn't larger than if it runs for much longer.
Making all programs in the test-suite run between 0.1 and 1 second would make the test-suite run probably between 1 and 2 orders of magnitude faster.
In these experiments, I see nbench taking between 0.5% and 3% of the total test-suite running time. So if it's little work to reduce the number of iterations in nbench as part of this work, we at least already have this test-suite speedup in the bank.

I will introduce an N_ITERATIONS define and reduce it from 5 to 1, which brings the runtime down to 1s on my desktop machine.

MultiSource/Benchmarks/nbench/nbench0.c

 *************/
 #ifdef MAC
 void main(void)
 #else
 int main(int argc, char *argv[])
 #endif
 {
 int i;                  /* Index */
+int iter;
 time_t time_and_date;   /* Self-explanatory */
 struct tm *loctime;
 double bmean;           /* Benchmark mean */
 double bstdev;          /* Benchmark stdev */
 double lx_memindex;     /* Linux memory index (mainly integer operations)*/
 double lx_intindex;     /* Linux integer index */
 double lx_fpindex;      /* Linux floating-point index */
 double intindex;        /* Integer index */

 output_string("--------------------:------------------:-------------:------------\n");
 #endif
 
 for(i=0;i<NUMTESTS;i++)
 {
         if(tests_to_do[i])
         {       sprintf(buffer,"%s    :",ftestnames[i]);
                                 output_string(buffer);
+#if 0
                 if (0!=bench_with_confidence(i,
                         &bmean,
                         &bstdev,
                         &bnumrun)){
-#if 0
       output_string("\n** WARNING: The current test result is NOT 95 % statistically certain.\n");
       output_string("** WARNING: The variation among the individual results is too large.\n");
       output_string("                    :");
+    }
 #endif
-    }
+                for (unsigned iter = 0; iter < 5; ++iter) {
+                  (*funcpointer[i])();
+                }
 #ifdef LINUX
                 sprintf(buffer," %15.5g  :  %9.2f  :  %9.2f\n",
                         bmean,bmean/bindex[i],bmean/lx_bindex[i]);
 #else
     sprintf(buffer,"  Iterations/sec.: %13.2f  Index: %6.2f\n",
                         /*bmean,bmean/bindex[i],*/ 0.0, 0.0);
 #endif
                 output_string(buffer);

MultiSource/Benchmarks/nbench/sysspec.h

 ** this code.
 */
 
 /*
 ** Standard includes
 */
 #include <stdlib.h>
 #include <stdio.h>
-#include <time.h>
 #include <string.h>
 
 #include "nmglobal.h"
 
 #if 0 /*!defined(__APPLE__)*/
 #include <malloc.h>
 #endif
 

MultiSource/Benchmarks/nbench/sysspec.c

 
 /****************************
 ** StartStopwatch
 ** Starts a software stopwatch.  Returns the first value of
 ** the stopwatch in ticks.
 */
 unsigned long StartStopwatch()
 {
-#ifdef MACTIMEMGR
-/*
-** For Mac code warrior, use timer. In this case, what we return is really
-** a dummy value.
-*/
-InsTime((QElemPtr)&myTMTask);
-PrimeTime((QElemPtr)&myTMTask,-MacHSTdelay);
-return((unsigned long)1);
-#else
-#ifdef WIN31TIMER
-/*
-** Win 3.x timer returns a DWORD, which we coax into a long.
-*/
-_Call16(lpfn,"p",&win31tinfo);
-return((unsigned long)win31tinfo.dwmsSinceStart);
-#else
-return((unsigned long)clock());
-#endif
-#endif
+  /* no timing code in this version. */
+  return 0;
 }
 
 /****************************
 ** StopStopwatch
 ** Stops the software stopwatch.  Expects as an input argument
 ** the stopwatch start time.
 */
 unsigned long StopStopwatch(unsigned long startticks)
 {
-  
-#ifdef MACTIMEMGR
-/*
-** For Mac code warrior...ignore startticks.  Return val. in microseconds
-*/
-RmvTime((QElemPtr)&myTMTask);
-return((unsigned long)(MacHSTdelay+myTMTask.tmCount-MacHSTohead));
-#else
-#ifdef WIN31TIMER
-_Call16(lpfn,"p",&win31tinfo);
-return((unsigned long)win31tinfo.dwmsSinceStart-startticks);
-#else
-return((unsigned long)clock()-startticks);
-#endif
-#endif
+  /* no timing code in this version. */
+  return 1000;
 }
 
 /****************************
 ** TicksToSecs
 ** Converts ticks to seconds.  Converts ticks to integer
 ** seconds, discarding any fractional amount.
 */
 unsigned long TicksToSecs(unsigned long tickamount)
 {
-#ifdef CLOCKWCT
-return((unsigned long)(tickamount/CLK_TCK));
-#endif
-
-#ifdef MACTIMEMGR
-/* +++ MAC time manager version (using timer in microseconds) +++ */
-return((unsigned long)(tickamount/1000000));
-#endif
-
-#ifdef CLOCKWCPS
-/* Everybody else */
-return((unsigned long)(tickamount/CLOCKS_PER_SEC));
-#endif
-
-#ifdef WIN31TIMER
-/* Each tick is 840 nanoseconds */
-return((unsigned long)(tickamount/1000L));
-#endif
-
+  /* no timing code in this version. */
+  return 0;
 }
 
 /****************************
 ** TicksToFracSecs
 ** Converts ticks to fractional seconds.  In other words,
 ** this returns the exact conversion from ticks to
 ** seconds.
 */
 double TicksToFracSecs(unsigned long tickamount)
 {
-#ifdef CLOCKWCT
-return((double)tickamount/(double)CLK_TCK);
-#endif
-
-#ifdef MACTIMEMGR
-/* +++ MAC time manager version +++ */
-return((double)tickamount/(double)1000000);
-#endif
-
-#ifdef CLOCKWCPS
-/* Everybody else */
-return((double)tickamount/(double)CLOCKS_PER_SEC);
-#endif
-
-#ifdef WIN31TIMER
-/* Using 840 nanosecond ticks */
-return((double)tickamount/(double)1000);
-#endif
+  /* no timing code in this version. */
+  return 0;
 }