Add math benchmark latency test

  Alexander Monakov wrote:
> I suggest using "reciprocal throughput" if you're looking for a short term
> for 'independent executions per unit time'.  It's easier to recognize and
> already used in practice (e.g. in docs by Agner Fog).

Right what about this?

   "workload-spec2006.wrf": {
    "reciprocal throughput (ns)": 20,
    "latency (ns)": 50,
    "throughput (iters/s)": 5.0e+07
   }

This leads to a question, some targets use an odd header hp-timing.h. What units
does this use? Or is it completely undefined (and could potentially change between
GLIBC versions)?


ChangeLog:
2017-08-16  Wilco Dijkstra  <wdijkstr@arm.com>
  
        * benchtests/bench-skeleton.c (main): Add support for
        latency benchmarking.
        * benchtests/scripts/bench.py: Add support for latency benchmarking.
--
  

On Wednesday 16 August 2017 08:52 PM, Wilco Dijkstra wrote:
> Alexander Monakov wrote:
>> I suggest using "reciprocal throughput" if you're looking for a short term
>> for 'independent executions per unit time'.  It's easier to recognize and
>> already used in practice (e.g. in docs by Agner Fog).
> 
> Right what about this?
> 
>    "workload-spec2006.wrf": {
>     "reciprocal throughput (ns)": 20,
>     "latency (ns)": 50,
>     "throughput (iters/s)": 5.0e+07

Please drop the spaces and special chars in the key names; they need to
validate against benchout.schema and IIRC it doesn't allow spaces.
Simple reciprocal-throughput, latency, etc. ought to be sufficient.

>    }
> 
> This leads to a question, some targets use an odd header hp-timing.h. What units
> does this use? Or is it completely undefined (and could potentially change between
> GLIBC versions)?

These change between architectures and may change between glibc versions
if an architecture adds a hardware time source read later for example.

Siddhesh

> 
> 
> ChangeLog:
> 2017-08-16  Wilco Dijkstra  <wdijkstr@arm.com>
>   
>         * benchtests/bench-skeleton.c (main): Add support for
>         latency benchmarking.
>         * benchtests/scripts/bench.py: Add support for latency benchmarking.
> --
> 
> diff --git a/benchtests/bench-skeleton.c b/benchtests/bench-skeleton.c
> index 3c6dad705594ac0a53edcb4e09686252c13127cf..48287be93b432b3acfc2431d1f7959bd00815b3b 100644
> --- a/benchtests/bench-skeleton.c
> +++ b/benchtests/bench-skeleton.c
> @@ -71,8 +71,10 @@ main (int argc, char **argv)
>        bool is_bench = strncmp (VARIANT (v), "workload-", 9) == 0;
>        double d_total_i = 0;
>        timing_t total = 0, max = 0, min = 0x7fffffffffffffff;
> +      timing_t throughput = 0, latency = 0;
>        int64_t c = 0;
>        uint64_t cur;
> +      BENCH_VARS;
>        while (1)
>  	{
>  	  if (is_bench)
> @@ -86,7 +88,16 @@ main (int argc, char **argv)
>  		  BENCH_FUNC (v, i);
>  	      TIMING_NOW (end);
>  	      TIMING_DIFF (cur, start, end);
> -	      TIMING_ACCUM (total, cur);
> +	      TIMING_ACCUM (throughput, cur);
> +
> +	      TIMING_NOW (start);
> +	      for (k = 0; k < iters; k++)
> +		for (i = 0; i < NUM_SAMPLES (v); i++)
> +		  BENCH_FUNC_LAT (v, i);
> +	      TIMING_NOW (end);
> +	      TIMING_DIFF (cur, start, end);
> +	      TIMING_ACCUM (latency, cur);
> +
>  	      d_total_i += iters * NUM_SAMPLES (v);
>  	    }
>  	  else
> @@ -131,12 +142,18 @@ main (int argc, char **argv)
>        /* Begin variant.  */
>        json_attr_object_begin (&json_ctx, VARIANT (v));
>  
> -      json_attr_double (&json_ctx, "duration", d_total_s);
> -      json_attr_double (&json_ctx, "iterations", d_total_i);
>        if (is_bench)
> -	json_attr_double (&json_ctx, "throughput", d_total_s / d_total_i);
> +	{
> +	  json_attr_double (&json_ctx, "reciprocal throughput (ns)",
> +			    throughput / d_total_i);
> +	  json_attr_double (&json_ctx, "latency (ns)", latency / d_total_i);
> +	  json_attr_double (&json_ctx, "throughput (iters/s)",
> +			    d_total_i / throughput * 1000000000.0);
> +	}
>        else
>  	{
> +	  json_attr_double (&json_ctx, "duration", d_total_s);
> +	  json_attr_double (&json_ctx, "iterations", d_total_i);
>  	  json_attr_double (&json_ctx, "max", max / d_iters);
>  	  json_attr_double (&json_ctx, "min", min / d_iters);
>  	  json_attr_double (&json_ctx, "mean", d_total_s / d_total_i);
> diff --git a/benchtests/scripts/bench.py b/benchtests/scripts/bench.py
> index 8c1c9eeb2bc67a16cb8a8e010fd2b8a2ef8ab6df..b7ccb7c8c2bf1822202a2377dfb0675516115cc5 100755
> --- a/benchtests/scripts/bench.py
> +++ b/benchtests/scripts/bench.py
> @@ -45,7 +45,7 @@ DEFINES_TEMPLATE = '''
>  # variant is represented by the _VARIANT structure.  The ARGS structure
>  # represents a single set of arguments.
>  STRUCT_TEMPLATE = '''
> -#define CALL_BENCH_FUNC(v, i) %(func)s (%(func_args)s)
> +#define CALL_BENCH_FUNC(v, i, x) %(func)s (x %(func_args)s)
>  
>  struct args
>  {
> @@ -84,7 +84,9 @@ EPILOGUE = '''
>  #define RESULT(__v, __i) (variants[(__v)].in[(__i)].timing)
>  #define RESULT_ACCUM(r, v, i, old, new) \\
>          ((RESULT ((v), (i))) = (RESULT ((v), (i)) * (old) + (r)) / ((new) + 1))
> -#define BENCH_FUNC(i, j) ({%(getret)s CALL_BENCH_FUNC (i, j);})
> +#define BENCH_FUNC(i, j) ({%(getret)s CALL_BENCH_FUNC (i, j, );})
> +#define BENCH_FUNC_LAT(i, j) ({%(getret)s CALL_BENCH_FUNC (i, j, %(latarg)s);})
> +#define BENCH_VARS %(defvar)s
>  #define FUNCNAME "%(func)s"
>  #include "bench-skeleton.c"'''
>  
> @@ -122,17 +124,22 @@ def gen_source(func, directives, all_vals):
>      # If we have a return value from the function, make sure it is
>      # assigned to prevent the compiler from optimizing out the
>      # call.
> +    getret = ''
> +    latarg = ''
> +    defvar = ''
> +
>      if directives['ret']:
>          print('static %s volatile ret;' % directives['ret'])
> -        getret = 'ret = '
> -    else:
> -        getret = ''
> +        print('static %s zero __attribute__((used)) = 0;' % directives['ret'])
> +        getret = 'ret = func_res = '
> +        latarg = 'func_res * zero +'
> +        defvar = '%s func_res = 0;' % directives['ret']
>  
>      # Test initialization.
>      if directives['init']:
>          print('#define BENCH_INIT %s' % directives['init'])
>  
> -    print(EPILOGUE % {'getret': getret, 'func': func})
> +    print(EPILOGUE % {'getret': getret, 'func': func, 'latarg': latarg, 'defvar': defvar })
>  
>  
>  def _print_arg_data(func, directives, all_vals):
>     
>