Re: [igt-dev] [Intel-gfx] [PATCH i-g-t v2] benchmarks/gem_wsim: Manually calculate VLA struct sizes

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 24/05/2019 09:45, 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. So calculate the size by hand!
> 
> v2: Use alloca().
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   benchmarks/gem_wsim.c | 115 +++++++++++++++++++++++-------------------
>   1 file changed, 64 insertions(+), 51 deletions(-)
> 
> diff --git a/benchmarks/gem_wsim.c b/benchmarks/gem_wsim.c
> index e2ffb93a9..db19925b1 100644
> --- a/benchmarks/gem_wsim.c
> +++ b/benchmarks/gem_wsim.c
> @@ -1441,6 +1441,29 @@ 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;
> +
> +	return sizeof(*ptr) + count * sizeof(ptr->engines[0]);
> +}
> +
> +static size_t sizeof_param_engines(int count)
> +{
> +	struct i915_context_param_engines *ptr;
> +
> +	return sizeof(*ptr) + count * sizeof(ptr->engines[0]);
> +}
> +
> +static size_t sizeof_engines_bond(int count)
> +{
> +	struct i915_context_engines_bond *ptr;
> +
> +	return sizeof(*ptr) + count * sizeof(ptr->engines[0]);
> +}
> +
> +#define alloca0(sz) ({ size_t sz__ = (sz); memset(alloca(sz__), 0, sz__); })
> +
>   static int
>   prepare_workload(unsigned int id, struct workload *wrk, unsigned int flags)
>   {
> @@ -1676,66 +1699,54 @@ 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 =
> +				alloca0(sizeof_param_engines(ctx->engine_map_count + 1));
> +			struct i915_context_engines_load_balance *load_balance =
> +				alloca0(sizeof_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 =
> +					alloca0(sizeof_engines_bond(__builtin_popcount(mask)));
>   				unsigned int b, e;
>   
> -				prev = p;
> -				p = alloca(sizeof(bond));
> -				assert(p);
> -				memset(p, 0, sizeof(bond));
> +				bond->base.next_extension = to_user_pointer(last);
> +				bond->base.name = I915_CONTEXT_ENGINES_EXT_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);
> -
> -				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;
> @@ -1743,42 +1754,44 @@ 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);
>   		} 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 =
> +				alloca0(sizeof_load_balance(count));
> +			struct i915_context_param_engines *set_engines =
> +				alloca0(sizeof_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);
>   		}
> 

Seems correct.

You couldn't resist throwing in the reverse bond list building 
simplification as well. :)

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
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