Re: [dpdk-dev] [PATCH 1/4] test/stack: avoid trivial memory allocations

["Eads, Gage" <gage.eads@intel.com>]

> -----Original Message-----
> From: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Sent: Tuesday, August 11, 2020 3:50 PM
> To: Stephen Hemminger <stephen@networkplumber.org>; Eads, Gage
> <gage.eads@intel.com>
> Cc: Steven Lariau <Steven.Lariau@arm.com>; Olivier Matz
> <olivier.matz@6wind.com>; dev@dpdk.org; Dharmik Thakkar
> <Dharmik.Thakkar@arm.com>; nd <nd@arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: RE: [dpdk-dev] [PATCH 1/4] test/stack: avoid trivial memory
> allocations
> 
> <snip>
> 
> > > >
> > > > Replace the arguments array by one argument.
> > > > All objects in the args array have the same values, so there is no
> > > > need to use an array, only one struct is enough.
> > > > The args object is a lot smaller, and the allocation can be replaced
> > > > with a stack variable.
> > > >
> > > > The allocation of obj_table isn't needed either, because MAX_BULK is
> > > > small. The allocation can instead be replaced with a static array.
> > > >
> > > > Signed-off-by: Steven Lariau <steven.lariau@arm.com>
> > > > Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
> > > > Reviewed-by: Phil Yang <phil.yang@arm.com>
> > > > Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > > > ---
> > > >  app/test/test_stack.c | 39 ++++++---------------------------------
> > > >  1 file changed, 6 insertions(+), 33 deletions(-)
> > > >
> > > > diff --git a/app/test/test_stack.c b/app/test/test_stack.c index
> > > > c8dac1f55..5a7273a7d 100644
> > > > --- a/app/test/test_stack.c
> > > > +++ b/app/test/test_stack.c
> > > > @@ -280,16 +280,9 @@ static int
> > > >  stack_thread_push_pop(void *args)
> > > >  {
> > > >  	struct test_args *t = args;
> > > > -	void **obj_table;
> > > > +	void *obj_table[MAX_BULK];
> > > >  	int i;
> > > >
> > > > -	obj_table = rte_calloc(NULL, STACK_SIZE, sizeof(void *), 0);
> > > > -	if (obj_table == NULL) {
> > > > -		printf("[%s():%u] failed to calloc %zu bytes\n",
> > > > -		       __func__, __LINE__, STACK_SIZE * sizeof(void *));
> > > > -		return -1;
> > > > -	}
> > > > -
> > > >  	for (i = 0; i < NUM_ITERS_PER_THREAD; i++) {
> > > >  		unsigned int success, num;
> > > >
> > > > @@ -310,28 +303,25 @@ stack_thread_push_pop(void *args)
> > > >  		if (rte_stack_push(t->s, obj_table, num) != num) {
> > > >  			printf("[%s():%u] Failed to push %u pointers\n",
> > > >  			       __func__, __LINE__, num);
> > > > -			rte_free(obj_table);
> > > >  			return -1;
> > > >  		}
> > > >
> > > >  		if (rte_stack_pop(t->s, obj_table, num) != num) {
> > > >  			printf("[%s():%u] Failed to pop %u pointers\n",
> > > >  			       __func__, __LINE__, num);
> > > > -			rte_free(obj_table);
> > > >  			return -1;
> > > >  		}
> > > >
> > > >  		rte_atomic64_sub(t->sz, num);
> > > >  	}
> > > >
> > > > -	rte_free(obj_table);
> > > >  	return 0;
> > > >  }
> > >
> > > Agreed, the dynamic allocation is unnecessary.
> > >
> > > >
> > > >  static int
> > > >  test_stack_multithreaded(uint32_t flags)  {
> > > > -	struct test_args *args;
> > > > +	struct test_args args;
> > > >  	unsigned int lcore_id;
> > > >  	struct rte_stack *s;
> > > >  	rte_atomic64_t size;
> > > > @@ -344,45 +334,28 @@ test_stack_multithreaded(uint32_t flags)
> > > >  	printf("[%s():%u] Running with %u lcores\n",
> > > >  	       __func__, __LINE__, rte_lcore_count());
> > > >
> > > > -	args = rte_malloc(NULL, sizeof(struct test_args) * RTE_MAX_LCORE,
> > > > 0);
> > > > -	if (args == NULL) {
> > > > -		printf("[%s():%u] failed to malloc %zu bytes\n",
> > > > -		       __func__, __LINE__,
> > > > -		       sizeof(struct test_args) * RTE_MAX_LCORE);
> > > > -		return -1;
> > > > -	}
> > > > -
> > > >  	s = rte_stack_create("test", STACK_SIZE, rte_socket_id(), flags);
> > > >  	if (s == NULL) {
> > > >  		printf("[%s():%u] Failed to create a stack\n",
> > > >  		       __func__, __LINE__);
> > > > -		rte_free(args);
> > > >  		return -1;
> > > >  	}
> > > >
> > > >  	rte_atomic64_init(&size);
> > > > +	args.s = s;
> > > > +	args.sz = &size;
> > > >
> > > >  	RTE_LCORE_FOREACH_SLAVE(lcore_id) {
> > > > -		args[lcore_id].s = s;
> > > > -		args[lcore_id].sz = &size;
> > > > -
> > > >  		if (rte_eal_remote_launch(stack_thread_push_pop,
> > > > -					  &args[lcore_id], lcore_id))
> > > > +					  &args, lcore_id))
> > > >  			rte_panic("Failed to launch lcore %d\n", lcore_id);
> > > >  	}
> > >
> > >
> > > In general we shouldn't pass a stack variable to other threads. Though
> > > your code here looks fine, I'd rather err on the safe side in case
> > > this is ever used as a template/basis for some other
> > > code...particularly since there's no performance/correctness/etc.
> penalty to
> > using dynamically allocated memory.
> > >
> > > To support patch 2/4, you can instead convert the rte_malloc to
> > > allocate a single shared test_args structure. Or perhaps move patch 4
> > > earlier in the series, and simply pass the stack pointer instead.
> > >
> > > Thanks,
> > > Gage
> >
> > There is no gain to using rte_malloc unless you are doing
> primary/secondary
> > process or trying to test rte_malloc. Why not use regular malloc which has
> > good tools and library support.
> 
> I think making 'args' a global variable is enough in this case.

Agreed.

Thanks,
Gage