Re: [PATCH] rs6000: Parameterize some const values for density test

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2021/9/18 上午6:26, Segher Boessenkool wrote:
> Hi!
> 
> On Wed, Sep 15, 2021 at 04:52:49PM +0800, Kewen.Lin wrote:
>> This patch follows the discussion here[1], where Segher suggested
>> parameterizing those exact magic constants for density heuristics,
>> to make it easier to tweak if need.
>>
>> Since these heuristics are quite internal, I make these parameters
>> as undocumented and be mainly used by developers.
> 
> Okido.
> 
>> +      if (data->nloads > (unsigned int) rs6000_density_load_num_threshold
>> +	  && load_pct > (unsigned int) rs6000_density_load_pct_threshold)
> 
> Those variables are unsigned int already.  Don't cast please.
> 

Unfortunately this is required by bootstrapping.  The UInteger for the
param definition is really confusing, in the underlying implementation
it's still "signed".  If you grep "(unsigned) param", you can see a few
examples.  I guess the "UInteger" is mainly for the param value range
checking.

>> +-param=rs6000-density-pct-threshold=
>> +Target Undocumented Joined UInteger Var(rs6000_density_pct_threshold) Init(85) IntegerRange(0, 99) Param
> 
> So make this and all other percentages (0, 100) please.
> 

I thought 99 is enough for the RHS in ">". just realized it's more clear
with 100.  Will fix!

>> +When costing for loop vectorization, we probably need to penalize the loop body cost if the existing cost model may not adequately reflect delays from unavailable vector resources.  We collect the cost for vectorized statements and non-vectorized statements separately, check the proportion of vec_cost to total cost of vec_cost and non vec_cost, and penalize only if the proportion exceeds the threshold specified by this parameter.  The default value is 85.
> 
> It would be good if we can use line breaks in the source code for things
> like this, but I don't think we can.  This message is mainly used for
> "--help=param", and it is good there to have as short messages as you
> can.  But given the nature of params you need quite a few words often,
> and you do not want to say so little that things are no clear, either.
> 
> So, dunno :-)

I did some testings, the line breaks writing can still survive in the
"--help=param" show, the lines are concatenated with " ".  Although
there seems no this kind of writing practices, I am guessing you want
me to do line breaks for their descriptions?  If so, I will make them
short as the above "Target Undocumented..." line.  Or do you want it
to align source code ColumnLimit 80 (for these cases, it would look
shorter)?

> 
> Oksy for trunk with these fixes and what Bill mentioned in the other
> thread.  Thanks!
> 

OK, thanks again!

BR,
Kewen