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Subject: Re: [boost] Proposal: Monotonic Containers - Comparison with boost::pool, boost::fast_pool and TBB
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-06-22 18:36:35


Christian Schladetsch wrote:
> Hi Luke,
> [...]
>> Luke> Peak memory will be a good metric. Do you have access to VTune? You
>> seem to struggle to identify the cause of performance loss and are reduced
>> to guesswork.
> Peak memory measured by an external tool is no good, as boost::pool and
> boost::fast_pool both leak memory. I need to be able to sample the memory
> used at certain times in the application in a cross-platform way. I'll get
> to this in due time.
> I have been focused on getting the benchmark results more than attempting to
> do a complete analysis of their implications. The latest results are here
> I still can't explain why monotonic is faster at
> sorting a 500,000 element pre-reserved vector, but I have only reported the
> result and have not investigated deeply.
> I have added mean, standard deviation, min and max factors for each of the
> small, medium, and large benchmark sets. I print a cumulative total at the
> end of each set, and a summary of all results at the end. These summaries
> are:
> GCC:
> scheme mean std-dev min max
> fast 36.3 173 0.25 1.63e+03
> pool 27.8 1.02e+04 0.857 897
> std 1.69 0.91 0.333 5
> tbb 1.59 0.849 0.333 5
> scheme mean std-dev min max
> fast 35.4 132 0.603 1.32e+003
> pool 27.1 1.13e+004 0.693 878
> std 2.7 1.7 0.628 7
> tbb 1.44 0.727 0.291 6.4
> The mean is the average speedup factor provided by monotonic allocation over
> the given scheme. So for MSVC, summarised over all tests, monotonic is 1.4X
> faster than TBB with a standard deviation of 0.7. TBB was 3.4X faster at its
> best and 6.4X slower at its worst.
> Note that monotonic was on average 35X faster than boost::fast_pool, but
> notice too that the standard deviation is very high. At its worst, fast_pool
> was 1,300X slower than monotonic and at its best was 1.6X faster.
> boost::pool faired little better, with an even worse standard deviation of
> 10,000(!). One could argue that the tests are skewed, so I invite you to
> look at them and suggest any changes or additions. See
> for all the tests, and
> the test harness.
> It is no surprise that TBB performs best across both platforms with the
> smallest standard deviation.

I'm not convinced that the average is meaningful.
boost::fast_pool_allocator is not intended to be used
with std::vector. You're averaging many cases for
which it is documented to behave badly with a couple
of cases for which it is fine. Also, even though pool_allocator
is supposed to work with std::vector, it is slow as I would
expect. The pool data structure is really designed for
fixed size allocations and I for one am not particularly
enamored of the idea of using it for std::vector.

Also, this is completely unreleated, but for lines like this

      fast 1.49 0.838 0.603 1.32e+003

It looks like the cumulative min/max are being used instead of
the local min/max.

In Christ,
Steven Watanabe

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