Re: [PATCH] Add malloc micro benchmark

[DJ Delorie <dj@redhat.com>]

Looks good to me, although I'd like some additional comments in the test
code.

Wilco Dijkstra <Wilco.Dijkstra@arm.com> writes:
> -bench-malloc := malloc-thread
> +bench-malloc := malloc-thread malloc-simple

Adding a test, ok

> -$(objpfx)bench-malloc-thread: $(shared-thread-library)
> +$(addprefix $(objpfx)bench-,$(bench-malloc)): $(shared-thread-library)

Accepting a list of tests, ok

> -   malloc-thread
> +   malloc-thread malloc-simple

Adding a test, ok

>  bench-malloc: $(binaries-bench-malloc)
>  	for run in $^; do \
> +	  echo "$${run}"; \
> +	  if [ `basename $${run}` = "bench-malloc-thread" ]; then \
>  		for thr in 1 8 16 32; do \
>  			echo "Running $${run} $${thr}"; \
> -	  $(run-bench) $${thr} > $${run}-$${thr}.out; \
> -	  done;\
> +			$(run-bench) $${thr} > $${run}-$${thr}.out; \
> +		done;\
> +	  else \
> +		for thr in 8 16 32 64 128 256 512 1024 2048 4096; do \
> +		  echo "Running $${run} $${thr}"; \
> +		  $(run-bench) $${thr} > $${run}-$${thr}.out; \
> +		done;\
> +	  fi;\
>  	done

I wonder if this could be done more elegantly, but I'm OK with a simple
approach for now.  If we end up adding many more such tests we might
need to revisit this part.

> +/* Benchmark malloc and free functions.
> +   Copyright (C) 2018 Free Software Foundation, Inc.

2019

> +
> +#include <pthread.h>

I would like to see a comment block somewhere in this code that
describes, to the casual future reader, what this test is looking for
and why it's different than other tests.  I won't hold up my OK for it,
though.

> +#define NUM_ITERS 1000000
> +#define NUM_ALLOCS 4
> +#define MAX_ALLOCS 1600

How long does this test take to run, on average, compared to other
tests?  Do we have to worry about increasing timeouts for slow hosts?

> +static void
> +do_benchmark (malloc_args *args, int **arr)
> +{
> +  timing_t start, stop;
> +  size_t iters = args->iters;
> +  size_t size = args->size;
> +  int n = args->n;
> +
> +  TIMING_NOW (start);
> +
> +  for (int j = 0; j < iters; j++)
> +    {
> +      for (int i = 0; i < n; i++)
> +	arr[i] = malloc (size);
> +
> +      for (int i = 0; i < n; i++)
> +	free (arr[i]);
> +    }
> +
> +  TIMING_NOW (stop);
> +
> +  TIMING_DIFF (args->elapsed, start, stop);
> +}

Simple loop, but doesn't test for malloc returning NULL.

> +  /* Run benchmark single threaded in main_arena.  */
> +  for (int i = 0; i < NUM_ALLOCS; i++)
> +    do_benchmark (&tests[0][i], arr);
> +
> +  /* Run benchmark in a thread_arena.  */
> +  pthread_t t;
> +  pthread_create (&t, NULL, thread_test, (void*)arr);
> +  pthread_join (t, NULL);
> +
> +  /* Repeat benchmark in main_arena with SINGLE_THREAD_P == false.  */
> +  for (int i = 0; i < NUM_ALLOCS; i++)
> +    do_benchmark (&tests[1][i], arr);

So we repeat the "main thread" case but now the heap is "messy" from the
now-joined thread... ok.