[erlang-questions] Hipe and Binary - Bitstring

[Kostis Sagonas]

On 3/27/19 1:04 PM, John Högberg wrote:
> Hi Oliver,
> 
> I've tried to reproduce this discrepancy on my machine, but I can only 
> see a modest difference on latest OTP 21 (the results are in microseconds):
> 
> Erlang/OTP 21 [erts-10.3.1] [source] [64-bit] [smp:24:24] [ds:24:24:10] [async-threads:1] [hipe]
> 
> 
> Eshell V10.3.1  (abort with ^G)
> 
> 1> c(t, []).
> 
> {ok,t}
> 
> 2> t:bench(one).
> 
> 15957304
> 
> 3> t:bench(union).
> 
> 559470
> 
> 4> c(t, [native]).
> 
> {ok,t}
> 
> 5> t:bench(one).
> 
> 3611371
> 
> 6> t:bench(union).
> 
> 501871
> 
> 
> I've attached the source code I used for this test, am I missing something?


We are obviously missing the benchmark program that Oliver used to get 
numbers.  But the "400x faster" figure cannot possibly be right.

Personally, I cannot see how one could turn function union/2, which is a 
one-liner with two bitstring matches and one construction, into a 
benchmark.  So, it's not surprising that the performance difference 
there is very small.

On the other hand, I would not call the performance difference between 
BEAM and HiPE that you observed "modest".  Four times faster execution 
is IMO something that deserves a better adjective.

Kostis


> On Wed, 2019-03-27 at 10:09 +0100, Oliver Bollmann wrote:
>>
>> I use, with binaries like <<1:1000000>>,
>>
>> one(F,<<Size:64/unsigned,Bitmap:Size/bitstring,_/bitstring>>) ->
>>    one(F,Bitmap,0,[]).
>> one(F, <<0:1,R/bitstring>>,N,Acc) ->
>>    one(F,R,N +1,Acc);
>> one(F, <<1:1,R/bitstring>>,N,Acc) ->
>>    one(F,R,N +1, [F(N) |Acc]);
>> one(_, <<>>,_,Acc) ->Acc.
>> union(<<Size:64/unsigned,L:Size/unsigned,P/bitstring>>,
>>      <<Size:64/unsigned,R:Size/unsigned,_/bitstring>>) ->
>>    <<Size:64/unsigned, (L bor R):Size/unsigned,P/bitstring>>.
>>
>> and call this functions 1,000,000 times, this takes for 1,000 calls 
>> about 20 minutes,
>>
>> if i compile with native -compile([native,{hipe, o2}])it takes 3 
>> seconds for 1,000 calls, so it is about 400x faster !!
>>
>> OS: OSX
>>
>> What is the secret?
>>
>> -- 
>> Grüße
>> Oliver Bollmann
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