Re: [PATCH AArch64]Penalize vector cost for large loops with too many vect insns.

["Bin.Cheng" <amker dot cheng at gmail dot com>]

On Sat, Oct 15, 2016 at 3:07 AM, kugan
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi Bin,
>
> On 15/10/16 00:15, Bin Cheng wrote:
>>
>> +/* Test for likely overcommitment of vector hardware resources.  If a
>> +   loop iteration is relatively large, and too large a percentage of
>> +   instructions in the loop are vectorized, the cost model may not
>> +   adequately reflect delays from unavailable vector resources.
>> +   Penalize the loop body cost for this case.  */
>> +
>> +static void
>> +aarch64_density_test (struct aarch64_vect_loop_cost_data *data)
>> +{
>> +  const int DENSITY_PCT_THRESHOLD = 85;
>> +  const int DENSITY_SIZE_THRESHOLD = 128;
>> +  const int DENSITY_PENALTY = 10;
>> +  struct loop *loop = data->loop_info;
>> +  basic_block *bbs = get_loop_body (loop);
>
>
> Is this worth being part of the cost model such that it can have different
> defaults for different micro-architecture?
Hi,
I don't know.  From my running, this penalizing function looks like a
quite benchmark specific tuning.  If that's the case, tuning for
different micro architecture may not give meaningful different
results, at the cost of three parameters.
Hi Bill,  I guess you are the original author?  Do you recall any
motivation of this code or have some comments?  Thanks very much.
Meanwhile, I can do some experiments on different AArch64 processors.

Thanks,
bin