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

Tvrtko Ursulin
2019-05-24T09:35:18Z

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