Re: [igt-dev] [PATCH i-g-t] benchmarks/gem_wsim: Heap allocate VLA structs

["Ser, Simon" <simon.ser@intel.com>]

On Fri, 2019-05-24 at 09:20 +0100, Tvrtko Ursulin wrote:
> On 24/05/2019 08:25, Chris Wilson wrote:
> > Apparently VLA structs (e.g. struct { int array[count] }) is a gcc
> > extension that clang refuses to support as handling memory layout is too
> > difficult for it.
> > 
> > Move the on-stack VLA to the heap.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > ---
> >   benchmarks/gem_wsim.c | 146 +++++++++++++++++++++++++++---------------
> >   1 file changed, 95 insertions(+), 51 deletions(-)
> > 
> > diff --git a/benchmarks/gem_wsim.c b/benchmarks/gem_wsim.c
> > index e2ffb93a9..0a0032bff 100644
> > --- a/benchmarks/gem_wsim.c
> > +++ b/benchmarks/gem_wsim.c
> > @@ -1441,6 +1441,48 @@ set_ctx_sseu(struct ctx *ctx, uint64_t slice_mask)
> >   	return slice_mask;
> >   }
> >   
> > +static size_t sizeof_load_balance(int count)
> > +{
> > +	struct i915_context_engines_load_balance *ptr;
> > +
> > +	assert(sizeof(ptr->engines[count]) == count * sizeof(ptr->engines[0]));
> 
> This seems wrong - is bound to trigger.
> 
> > +	return sizeof(*ptr) + sizeof(ptr->engines[count]);
> 
> So size of of engine needs to be multiplied by count.
> 
> > +}
> > +
> > +static struct i915_context_engines_load_balance *
> > +alloc_load_balance(int count)
> > +{
> > +	return calloc(1, sizeof_load_balance(count));
> 
> How about alloca so cleanup is simpler? Or is alloca also on the 
> unpopular list?
> 
> Or possibly what Simon suggested, just a large temporary stack arrays 
> would be enough and easiest diff. Just with an assert that it fits.
> 
> I can do that if you want?

I think Arek already has a patch for this.

> Regards,
> 
> Tvrtko
> 
> > +}
> > +
> > +static size_t sizeof_param_engines(int count)
> > +{
> > +	struct i915_context_param_engines *ptr;
> > +
> > +	assert(sizeof(ptr->engines[count]) == count * sizeof(ptr->engines[0]));
> > +	return sizeof(*ptr) + sizeof(ptr->engines[count]);
> > +}
> > +
> > +static struct i915_context_param_engines *
> > +alloc_param_engines(int count)
> > +{
> > +	return calloc(1, sizeof_param_engines(count));
> > +}
> > +
> > +static size_t sizeof_engines_bond(int count)
> > +{
> > +	struct i915_context_engines_bond *ptr;
> > +
> > +	assert(sizeof(ptr->engines[count]) == count * sizeof(ptr->engines[0]));
> > +	return sizeof(*ptr) + sizeof(ptr->engines[count]);
> > +}
> > +
> > +static struct i915_context_engines_bond *
> > +alloc_engines_bond(int count)
> > +{
> > +	return calloc(1, sizeof_engines_bond(count));
> > +}
> > +
> >   static int
> >   prepare_workload(unsigned int id, struct workload *wrk, unsigned int flags)
> >   {
> > @@ -1676,66 +1718,54 @@ prepare_workload(unsigned int id, struct workload *wrk, unsigned int flags)
> >   		}
> >   
> >   		if (ctx->engine_map) {
> > -			I915_DEFINE_CONTEXT_PARAM_ENGINES(set_engines,
> > -							  ctx->engine_map_count + 1);
> > -			I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(load_balance,
> > -								 ctx->engine_map_count);
> > +			struct i915_context_param_engines *set_engines =
> > +				alloc_param_engines(ctx->engine_map_count + 1);
> > +			struct i915_context_engines_load_balance *load_balance =
> > +				alloc_load_balance(ctx->engine_map_count);
> >   			struct drm_i915_gem_context_param param = {
> >   				.ctx_id = ctx_id,
> >   				.param = I915_CONTEXT_PARAM_ENGINES,
> > -				.size = sizeof(set_engines),
> > -				.value = to_user_pointer(&set_engines),
> > +				.size = sizeof_param_engines(ctx->engine_map_count + 1),
> > +				.value = to_user_pointer(set_engines),
> >   			};
> > +			struct i915_context_engines_bond *last = NULL;
> >   
> >   			if (ctx->wants_balance) {
> > -				set_engines.extensions =
> > -					to_user_pointer(&load_balance);
> > +				set_engines->extensions =
> > +					to_user_pointer(load_balance);
> >   
> > -				memset(&load_balance, 0, sizeof(load_balance));
> > -				load_balance.base.name =
> > +				load_balance->base.name =
> >   					I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE;
> > -				load_balance.num_siblings =
> > +				load_balance->num_siblings =
> >   					ctx->engine_map_count;
> >   
> >   				for (j = 0; j < ctx->engine_map_count; j++)
> > -					load_balance.engines[j] =
> > +					load_balance->engines[j] =
> >   						get_engine(ctx->engine_map[j]);
> > -			} else {
> > -				set_engines.extensions = 0;
> >   			}
> >   
> >   			/* Reserve slot for virtual engine. */
> > -			set_engines.engines[0].engine_class =
> > +			set_engines->engines[0].engine_class =
> >   				I915_ENGINE_CLASS_INVALID;
> > -			set_engines.engines[0].engine_instance =
> > +			set_engines->engines[0].engine_instance =
> >   				I915_ENGINE_CLASS_INVALID_NONE;
> >   
> >   			for (j = 1; j <= ctx->engine_map_count; j++)
> > -				set_engines.engines[j] =
> > +				set_engines->engines[j] =
> >   					get_engine(ctx->engine_map[j - 1]);
> >   
> > +			last = NULL;
> >   			for (j = 0; j < ctx->bond_count; j++) {
> >   				unsigned long mask = ctx->bonds[j].mask;
> > -				I915_DEFINE_CONTEXT_ENGINES_BOND(bond,
> > -								 __builtin_popcount(mask));
> > -				struct i915_context_engines_bond *p = NULL, *prev;
> > +				struct i915_context_engines_bond *bond =
> > +					alloc_engines_bond(__builtin_popcount(mask));
> >   				unsigned int b, e;
> >   
> > -				prev = p;
> > -				p = alloca(sizeof(bond));
> > -				assert(p);
> > -				memset(p, 0, sizeof(bond));
> > -
> > -				if (j == 0)
> > -					load_balance.base.next_extension =
> > -						to_user_pointer(p);
> > -				else if (j < (ctx->bond_count - 1))
> > -					prev->base.next_extension =
> > -						to_user_pointer(p);
> > +				bond->base.next_extension = to_user_pointer(last);
> > +				bond->base.name = I915_CONTEXT_ENGINES_EXT_BOND;
> >   
> > -				p->base.name = I915_CONTEXT_ENGINES_EXT_BOND;
> > -				p->virtual_index = 0;
> > -				p->master = get_engine(ctx->bonds[j].master);
> > +				bond->virtual_index = 0;
> > +				bond->master = get_engine(ctx->bonds[j].master);
> >   
> >   				for (b = 0, e = 0; mask; e++, mask >>= 1) {
> >   					unsigned int idx;
> > @@ -1743,44 +1773,58 @@ prepare_workload(unsigned int id, struct workload *wrk, unsigned int flags)
> >   					if (!(mask & 1))
> >   						continue;
> >   
> > -					idx = find_engine(&set_engines.engines[1],
> > +					idx = find_engine(&set_engines->engines[1],
> >   							  ctx->engine_map_count,
> >   							  e);
> > -					p->engines[b++] =
> > -						set_engines.engines[1 + idx];
> > +					bond->engines[b++] =
> > +						set_engines->engines[1 + idx];
> >   				}
> > +
> > +				last = bond;
> >   			}
> > +			load_balance->base.next_extension = to_user_pointer(last);
> >   
> >   			gem_context_set_param(fd, &param);
> > +
> > +			while (last) {
> > +				struct i915_context_engines_bond *next =
> > +					from_user_pointer(last->base.next_extension);
> > +				free(last);
> > +				last = next;
> > +			}
> > +			free(load_balance);
> > +			free(set_engines);
> >   		} else if (ctx->wants_balance) {
> >   			const unsigned int count = num_engines_in_class(VCS);
> > -			I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(load_balance,
> > -								 count);
> > -			I915_DEFINE_CONTEXT_PARAM_ENGINES(set_engines,
> > -							  count + 1);
> > +			struct i915_context_engines_load_balance *load_balance =
> > +				alloc_load_balance(count);
> > +			struct i915_context_param_engines *set_engines =
> > +				alloc_param_engines(count + 1);
> >   			struct drm_i915_gem_context_param param = {
> >   				.ctx_id = ctx_id,
> >   				.param = I915_CONTEXT_PARAM_ENGINES,
> > -				.size = sizeof(set_engines),
> > -				.value = to_user_pointer(&set_engines),
> > +				.size = sizeof_param_engines(count + 1),
> > +				.value = to_user_pointer(set_engines),
> >   			};
> >   
> > -			set_engines.extensions = to_user_pointer(&load_balance);
> > +			set_engines->extensions = to_user_pointer(load_balance);
> >   
> > -			set_engines.engines[0].engine_class =
> > +			set_engines->engines[0].engine_class =
> >   				I915_ENGINE_CLASS_INVALID;
> > -			set_engines.engines[0].engine_instance =
> > +			set_engines->engines[0].engine_instance =
> >   				I915_ENGINE_CLASS_INVALID_NONE;
> > -			fill_engines_class(&set_engines.engines[1], VCS);
> > +			fill_engines_class(&set_engines->engines[1], VCS);
> >   
> > -			memset(&load_balance, 0, sizeof(load_balance));
> > -			load_balance.base.name =
> > +			load_balance->base.name =
> >   				I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE;
> > -			load_balance.num_siblings = count;
> > +			load_balance->num_siblings = count;
> >   
> > -			fill_engines_class(&load_balance.engines[0], VCS);
> > +			fill_engines_class(&load_balance->engines[0], VCS);
> >   
> >   			gem_context_set_param(fd, &param);
> > +
> > +			free(set_engines);
> > +			free(load_balance);
> >   		}
> >   
> >   		if (wrk->sseu) {
> > 
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