[Mesa-dev] [PATCH] ra: Disable round-robin strategy for optimistically colorable nodes.

[Connor Abbott]

On Tue, Feb 17, 2015 at 2:00 PM, Jason Ekstrand <jason at jlekstrand.net> wrote:
>
>
> On Mon, Feb 16, 2015 at 11:39 AM, Francisco Jerez <currojerez at riseup.net>
> wrote:
>
>
> UINT_MAX would be clearer than ~0
>
>>
>>     int i;
>>
>>     while (progress) {
>> @@ -483,12 +490,16 @@ ra_simplify(struct ra_graph *g)
>>
>>        if (!progress && best_optimistic_node != ~0U) {
>
>
> I guess we're using ~0 other places... oh well...

Grr, this one is my fault... Francisco, feel free to fix this in a
follow-up patch if you want.

>
>>
>>          decrement_q(g, best_optimistic_node);
>> +         stack_optimistic_start =
>> +            MIN2(stack_optimistic_start, g->stack_count);
>
>
> It might be clearer to explicitly use an if here instead of the MIN2 because
> what this really means is "if (stack_optimistic_start == ~0)
> stack_optimistic_start = g->stack_count;"

I agree with this one.

>
> Other than that (and connor's comment), it looks fine to me.
>
> --Jason
>
>>
>>          g->stack[g->stack_count] = best_optimistic_node;
>>          g->stack_count++;
>>          g->nodes[best_optimistic_node].in_stack = true;
>>          progress = true;
>>        }
>>     }
>> +
>> +   g->stack_optimistic_start = stack_optimistic_start;
>>  }
>>
>>  /**
>> @@ -542,7 +553,16 @@ ra_select(struct ra_graph *g)
>>        g->nodes[n].reg = r;
>>        g->stack_count--;
>>
>> -      if (g->regs->round_robin)
>> +      /* Rotate the starting point except for optimistically colorable
>> nodes.
>> +       * The likelihood that we will succeed at allocating optimistically
>> +       * colorable nodes is highly dependent on the way that the previous
>> +       * nodes popped off the stack are laid out.  The round-robin
>> strategy
>> +       * increases the fragmentation of the register file and decreases
>> the
>> +       * number of nearby nodes assigned to the same color, what
>> increases the
>> +       * likelihood of spilling with respect to the dense packing
>> strategy.
>> +       */
>> +      if (g->regs->round_robin &&
>> +          g->stack_count <= g->stack_optimistic_start)
>>           start_search_reg = r + 1;
>>     }
>>
>> --
>> 2.1.3
>>
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>
>
>
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