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Subject: Re: [boost] Proposal: Monotonic Containers - Comparison with boost::pool, boost::fast_pool and TBB
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2009-06-19 12:30:09

Christian Schladetsch wrote:
>> Updated tests (more of them, better formatting of results) for
>> here for GCC and here
>> for
>> MSVC. I also added a column for std::allocator/mono.
> Have added comparison against TBB, as requested. These results are at
> the same location as linked to above.

Note tbb is pretty much the fastest established allocator. It does reuse memory and deallocation is not a no-op, so it is more general than monotonic, which must be scoped and cannot be used when volume of memory allocations greatly exceeds the maximum ammount of memory actually in use at any given time. In windows, monotonic is almost a wash with tbb, whereas in linux the difference between montotinic and tbb is not that great and hard to evaluate because the measurements lack precision.

The measurements shown are often only accurate to one significant digit, or don't register at all. Either get a more accurate timer or run larger benchmarks. Also, it is conventional to report speedup as a factor, rather than a percent. Instead of saying monotonic is 150% faster than std allocator you should report 1.5X as fast. This way instead of saying it is 1.9e+004% faster than fast_pool for thrash_pool_sort with length 510 you would say it is 190X faster, which just makes more sense all around. Also it makes more sense to say 0.95X as fast than 95% faster because it is more clear that values less than one are bad. People will trust benchmark results more if they are reported in a conventional manner.

I'd suggest adding the google allocator to the list as well. You can expect it to perform about the same as tbb since that is what we have found in our testing.

These benchmarks look much better than what you've shown previously, but I'd like you to also look for industry standard bencharks for allocators, or industry standard benchmarks that you can use to compare allocators. It is obvious to me that monotonic should not be used in certain ways it wasn't designed for, like for all allocations by a long running program without ever freeing or reusing any memory it has allocated, but it is not obvious from your benchmarks. I'd like you to also compare peak memory in the benchmark results and not just runtime, since this is often what people care about when they are optimizing. If you only have 256GB of memory and your can't afford to swap you find yourself implementing all kinds of things differently than if you have a terabyte. People need to understand the drawbacks of your allocator, not just the advantages, and benchmarks showing high peak memory and swapping when the allocator is used in a context it wasn't intended for should make that clear.


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