std.allocator needs your help

[Andrei Alexandrescu]

On 9/24/13 9:58 AM, Peter Alexander wrote:
> On Tuesday, 24 September 2013 at 15:25:11 UTC, Andrei Alexandrescu wrote:
>>> What are they paying exactly? An extra arg to allocate that can probably
>>> be defaulted?
>>>   void[] allocate(size_t bytes, size_t align = this.alignment) shared;
>>
>> For allocating relatively small objects (say up to 32K), we're looking
>> at tens of cycles, no more. An extra argument needs to be passed
>> around and more importantly looked at and acted upon. At this level
>> it's a serious dent in the time budget.
>
> The cost of a few cycles really doesn't matter for memory allocation...
> If you are really allocating memory so frequently that those few extra
> cycles matter then you are probably going to be memory bound anyway.

It does. I'm not even going to argue this.

> I think this is a situation where you need to justify yourself with
> something concrete. Can you provide an example of some code whose
> performance is significantly impacted by the addition of an alignment
> parameter? It has to be "real code" that does something useful, not just
> a loop the continually calls allocate.

Strings.


Andrei