Re: [boost] Proposal: Monotonic Containers

Subject: Re: [boost] Proposal: Monotonic Containers
From: David Bergman (David.Bergman_at_[hidden])
Date: 2009-06-10 13:58:52

On Jun 10, 2009, at 1:49 PM, David Bergman wrote:

> On Jun 10, 2009, at 4:54 AM, Christian Schladetsch wrote:
>
>> Hi Artyom,
>>
>> You **must** return aligned pointers from allocators.
>>
>>
>> boost::monotonic does not allocate.
>
> I wonder what that 'allocator' of yours is for then? ;-)
>
> Of course it allocates. And you fail to align the start address,  
> which makes certain use cases crash on certain platforms. On Intel,  
> it "just" gives the user a worse performance when misaligned. This  
> is not aligned (pun intended...) with your overall goal to give the  
> developer a high-performance tool. But do not take my word for it, I  
> ran a test with your container, the attached sample program and got  
> around 33.3 picoseconds on average to perform an increment on an  
> aligned long compared to 35.6 picoseconds for a misaligned long,  
> i.e., some 8% difference. Actually, I got a bit more with other  
> operations.

In fact, the attached version is a very lenient one, since it does  
give proper alignment for a lot of iterations... I used prime number  
distributions in other samples. Nevertheless, this sample produced  
between 8% and 10% difference between the two cases. I can provide you  
with more information about the performance hit of using misaligned  
stuff if you want.

/David

> #include <assert.h>
> #include <stdlib.h>
> #include <string.h>
> #include <iostream>
>
> #include <boost/timer.hpp>
>
> #include <boost/monotonic/vector.h>
> #include <boost/monotonic/list.h>
> #include <boost/monotonic/map.h>
> #include <boost/monotonic/set.h>
>
> template<typename C>
> struct Foo {
>  long ord;
>  C c;
> };
>
>
> template<typename C>
> void test_loop()
> {
> 	boost::monotonic::inline_storage<100000> storage;
> 	boost::monotonic::vector<Foo<C> > vec(storage);
> 	const int LOOP_COUNT = 100000000;
> 	const int ELEM_COUNT = 1000;
> 	Foo<C> orig = { 'A', 65 };	
> 	vec.assign(ELEM_COUNT, orig);
> 	boost::timer timer;
> 	for (int i = 0; i < LOOP_COUNT; ++i)
> 	  ++vec[1 + i % (ELEM_COUNT - 2)].ord;
> 	double elapsed = timer.elapsed();
> 	std::cout << "Incrementing ord = " << 1000000000*elapsed/LOOP_COUNT  
> << " ps per iteration" << std::endl;
> }
>
> int main(int argc, const char* argv[])
> {
>  test_loop<char>();
>  test_loop<long>();
> }
>
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