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From Benjamin Bannier <benjamin.bann...@mesosphere.io>
Subject Re: Review Request 68490: Optimized `class Resources` with copy-on-write.
Date Tue, 04 Sep 2018 09:36:36 GMT

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This is an automatically generated e-mail. To reply, visit:
https://reviews.apache.org/r/68490/#review208295
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Have you benchmarked against a dedicated copy-on-write abstraction? I understand that the
current implementation which only copies when needed might be more performant, but it also
appears to carry a huge mental overhead to me as users of `Resources` need to always pay a
lot of attention to how used objects could be shared. Using a slightly safer copy-on-write
abstraction might introduce some overhead, but could IMO be much easier to use and reduced
the likelihood of subtle bugs. It would also help encapsulate low-level issues like `use_count`,
see e.g., https://wg21.cmeerw.net/lwg/issue2776, http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0521r0.html.

I imagine this could be useful elsewhere as well in the future.

Note that implementations like the one presented in https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Copy-on-write
which allow getting references to wrapped value are prone to subtle issues in user code. Not
directly giving users a reference requires a little more determination to introduce bugs.

Dummy:

    // UNTESTED AND BUGGY. FOR DEMONSTRATION PURPOSES ONLY ;)
    template <typename T> struct cow {
      // We can only construct from a value we need to wrap. All other constructors
      // should be deleted as needed.
      //
      // Verify with e.g., SFINAE that
      //
      //     static_assert(is_convertible_v<remove_cvref_t<U>, T>);
      template <typename U> explicit cow(U);
    
      // Allow assignments from a `cow` we own. All other assignment operators
      // should be deleted as needed. These operators need to internally synchronize
      // concurrent access to the wrapped value.
      cow &operator=(cow);
    
      // Non-mutable access to wrapped value.
      const T &operator->() const;
      const T& operator*() const;
    
      // Mutating access to the wrapped value. `F` is callable as `void(T&)` and
      // applied to the wrapped value immediately. Synchronizes internally.
      template <typename F> cow &mut(F) { return *this; }
    };
    
    void example() {
        cow<int> i(47);
        assert(*i == 47);
    
        i.mut([](int &x) { x = 11; });
        assert(*i == 11);
    }

- Benjamin Bannier


On Aug. 24, 2018, 12:13 a.m., Meng Zhu wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://reviews.apache.org/r/68490/
> -----------------------------------------------------------
> 
> (Updated Aug. 24, 2018, 12:13 a.m.)
> 
> 
> Review request for mesos and Benjamin Mahler.
> 
> 
> Bugs: MESOS-6765
>     https://issues.apache.org/jira/browse/MESOS-6765
> 
> 
> Repository: mesos
> 
> 
> Description
> -------
> 
> This patch lets `class Resources` only store shared
> pointers to the underlying resource objects, so that
> read-only filter operations such as `reserved()`,
> `unreserved()` and etc. can avoid making copies of
> the whole resource objects. Instead, only shared pointers
> are copied.
> 
> In write operations, we check if there are more than one
> references to the resource object. If so, a copy is made
> for safe mutation without affecting owners.
> 
> To maintain the usage abstraction that `class Resources`
> still holds resource objects, we utilize
> `boost::indirect_iterator` iterator adapter to deference
> the shared pointers as we iterate.
> 
> 
> Diffs
> -----
> 
>   include/mesos/resources.hpp 6f81b14f8bc090a144eeae8f15639c370366166d 
>   include/mesos/v1/resources.hpp 09110530da16678abf6bf6b308906dd8ccc8180a 
>   src/common/resources.cpp 0110c0ee3e810ad1c29dfa5507b13ebd5d0222a2 
>   src/v1/resources.cpp 228a7327ffe7934d37b56ee67b8be9ae1e119ca8 
> 
> 
> Diff: https://reviews.apache.org/r/68490/diff/1/
> 
> 
> Testing
> -------
> 
> make check
> 
> Did a quick test on Mac with an optimized build, running benchmark `HierarchicalAllocator_BENCHMARK_Test.ResourceLabels`,
here are the results of comparing "before" and "after". Note, DVFS is not fixed. And we only
did a partial run to verify the validity of the patch, full evaluation coming soon.
> 
> **Overall, 33% performance improvement for the 1st steup (1000 agents and 1 frameworks)
and 32% improvement for the first 50 iterarions of the 2nd setup (1000 agents and 50 frameworks).**
> 
> Before:
> 
> [ RUN      ] SlaveAndFrameworkCount/HierarchicalAllocator_BENCHMARK_Test.ResourceLabels/0
> 
> Using 1000 agents and 1 frameworks
> Added 1 frameworks in 1.220022ms
> Added 1000 agents in 465.045382ms
> round 0 allocate() took 54.803773ms to make 0 offers after filtering 1000 offers
> round 1 allocate() took 66.690456ms to make 0 offers after filtering 1000 offers
> 
> Using 1000 agents and 50 frameworks
> Added 50 frameworks in 1.40774ms
> Added 1000 agents in 460.562488ms
> round 0 allocate() took 155.500548ms to make 1000 offers after filtering 1000 offers
> round 1 allocate() took 155.194986ms to make 1000 offers after filtering 2000 offers
> round 2 allocate() took 160.706712ms to make 1000 offers after filtering 3000 offers
> round 3 allocate() took 156.701883ms to make 1000 offers after filtering 4000 offers
> round 4 allocate() took 164.246987ms to make 1000 offers after filtering 5000 offers
> round 5 allocate() took 160.791809ms to make 1000 offers after filtering 6000 offers
> round 6 allocate() took 166.064652ms to make 1000 offers after filtering 7000 offers
> round 7 allocate() took 162.177213ms to make 1000 offers after filtering 8000 offers
> round 8 allocate() took 166.620163ms to make 1000 offers after filtering 9000 offers
> round 9 allocate() took 167.970045ms to make 1000 offers after filtering 10000 offers
> round 10 allocate() took 166.189463ms to make 1000 offers after filtering 11000 offers
> round 11 allocate() took 170.863462ms to make 1000 offers after filtering 12000 offers
> round 12 allocate() took 172.260473ms to make 1000 offers after filtering 13000 offers
> round 13 allocate() took 170.553911ms to make 1000 offers after filtering 14000 offers
> round 14 allocate() took 235.764593ms to make 1000 offers after filtering 15000 offers
> round 15 allocate() took 247.250433ms to make 1000 offers after filtering 16000 offers
> round 16 allocate() took 276.932824ms to make 1000 offers after filtering 17000 offers
> round 17 allocate() took 248.888469ms to make 1000 offers after filtering 18000 offers
> round 18 allocate() took 193.890556ms to make 1000 offers after filtering 19000 offers
> round 19 allocate() took 195.105346ms to make 1000 offers after filtering 20000 offers
> round 20 allocate() took 194.447428ms to make 1000 offers after filtering 21000 offers
> round 21 allocate() took 205.486287ms to make 1000 offers after filtering 22000 offers
> round 22 allocate() took 199.241922ms to make 1000 offers after filtering 23000 offers
> round 23 allocate() took 200.885488ms to make 1000 offers after filtering 24000 offers
> round 24 allocate() took 216.132361ms to make 1000 offers after filtering 25000 offers
> round 25 allocate() took 210.638273ms to make 1000 offers after filtering 26000 offers
> round 26 allocate() took 232.397778ms to make 1000 offers after filtering 27000 offers
> round 27 allocate() took 239.633708ms to make 1000 offers after filtering 28000 offers
> round 28 allocate() took 225.829677ms to make 1000 offers after filtering 29000 offers
> round 29 allocate() took 245.143272ms to make 1000 offers after filtering 30000 offers
> round 30 allocate() took 248.630295ms to make 1000 offers after filtering 31000 offers
> round 31 allocate() took 262.147804ms to make 1000 offers after filtering 32000 offers
> round 32 allocate() took 251.109969ms to make 1000 offers after filtering 33000 offers
> round 33 allocate() took 263.92273ms to make 1000 offers after filtering 34000 offers
> round 34 allocate() took 268.422275ms to make 1000 offers after filtering 35000 offers
> round 35 allocate() took 273.830163ms to make 1000 offers after filtering 36000 offers
> round 36 allocate() took 283.25481ms to make 1000 offers after filtering 37000 offers
> round 37 allocate() took 366.400781ms to make 1000 offers after filtering 38000 offers
> round 38 allocate() took 382.202755ms to make 1000 offers after filtering 39000 offers
> round 39 allocate() took 337.266121ms to make 1000 offers after filtering 40000 offers
> round 40 allocate() took 381.033696ms to make 1000 offers after filtering 41000 offers
> round 41 allocate() took 365.941946ms to make 1000 offers after filtering 42000 offers
> round 42 allocate() took 379.527886ms to make 1000 offers after filtering 43000 offers
> round 43 allocate() took 425.661181ms to make 1000 offers after filtering 44000 offers
> round 44 allocate() took 455.86657ms to make 1000 offers after filtering 45000 offers
> round 45 allocate() took 506.943117ms to make 1000 offers after filtering 46000 offers
> round 46 allocate() took 681.880233ms to make 1000 offers after filtering 47000 offers
> round 47 allocate() took 860.932974ms to make 1000 offers after filtering 48000 offers
> round 48 allocate() took 960.272209ms to make 1000 offers after filtering 49000 offers
> round 49 allocate() took 1.907427057secs to make 0 offers after filtering 50000 offers
> round 50 allocate() took 2.157864654secs to make 0 offers after filtering 50000 offers
> 
> 
> After:
> 
> Using 1000 agents and 1 frameworks
> Added 1 frameworks in 404709ns
> Added 1000 agents in 245.162138ms
> round 0 allocate() took 38.498883ms to make 0 offers after filtering 1000 offers
> round 1 allocate() took 42.234898ms to make 0 offers after filtering 1000 offers
> 
> Using 1000 agents and 50 frameworks
> Added 50 frameworks in 1.441281ms
> Added 1000 agents in 261.923711ms
> round 0 allocate() took 121.706074ms to make 1000 offers after filtering 1000 offers
> round 1 allocate() took 150.465925ms to make 1000 offers after filtering 2000 offers
> round 2 allocate() took 273.549893ms to make 1000 offers after filtering 3000 offers
> round 3 allocate() took 199.248799ms to make 1000 offers after filtering 4000 offers
> round 4 allocate() took 133.865752ms to make 1000 offers after filtering 5000 offers
> round 5 allocate() took 130.828599ms to make 1000 offers after filtering 6000 offers
> round 6 allocate() took 134.385597ms to make 1000 offers after filtering 7000 offers
> round 7 allocate() took 135.810198ms to make 1000 offers after filtering 8000 offers
> round 8 allocate() took 126.128592ms to make 1000 offers after filtering 9000 offers
> round 9 allocate() took 144.794829ms to make 1000 offers after filtering 10000 offers
> round 10 allocate() took 162.533506ms to make 1000 offers after filtering 11000 offers
> round 11 allocate() took 159.22141ms to make 1000 offers after filtering 12000 offers
> round 12 allocate() took 174.739823ms to make 1000 offers after filtering 13000 offers
> round 13 allocate() took 171.095423ms to make 1000 offers after filtering 14000 offers
> round 14 allocate() took 186.876661ms to make 1000 offers after filtering 15000 offers
> round 15 allocate() took 177.021603ms to make 1000 offers after filtering 16000 offers
> round 16 allocate() took 165.970722ms to make 1000 offers after filtering 17000 offers
> round 17 allocate() took 162.016338ms to make 1000 offers after filtering 18000 offers
> round 18 allocate() took 138.698917ms to make 1000 offers after filtering 19000 offers
> round 19 allocate() took 144.556913ms to make 1000 offers after filtering 20000 offers
> round 20 allocate() took 155.689926ms to make 1000 offers after filtering 21000 offers
> round 21 allocate() took 149.952025ms to make 1000 offers after filtering 22000 offers
> round 22 allocate() took 135.98823ms to make 1000 offers after filtering 23000 offers
> round 23 allocate() took 132.520992ms to make 1000 offers after filtering 24000 offers
> round 24 allocate() took 143.325635ms to make 1000 offers after filtering 25000 offers
> round 25 allocate() took 153.313423ms to make 1000 offers after filtering 26000 offers
> round 26 allocate() took 169.889066ms to make 1000 offers after filtering 27000 offers
> round 27 allocate() took 188.969694ms to make 1000 offers after filtering 28000 offers
> round 28 allocate() took 176.132259ms to make 1000 offers after filtering 29000 offers
> round 29 allocate() took 186.754676ms to make 1000 offers after filtering 30000 offers
> round 30 allocate() took 166.346508ms to make 1000 offers after filtering 31000 offers
> round 31 allocate() took 172.557665ms to make 1000 offers after filtering 32000 offers
> round 32 allocate() took 169.874406ms to make 1000 offers after filtering 33000 offers
> round 33 allocate() took 190.470692ms to make 1000 offers after filtering 34000 offers
> round 34 allocate() took 184.328221ms to make 1000 offers after filtering 35000 offers
> round 35 allocate() took 222.081892ms to make 1000 offers after filtering 36000 offers
> round 36 allocate() took 203.134216ms to make 1000 offers after filtering 37000 offers
> round 37 allocate() took 217.490016ms to make 1000 offers after filtering 38000 offers
> round 38 allocate() took 257.449904ms to make 1000 offers after filtering 39000 offers
> round 39 allocate() took 252.468529ms to make 1000 offers after filtering 40000 offers
> round 40 allocate() took 229.433398ms to make 1000 offers after filtering 41000 offers
> round 41 allocate() took 251.920859ms to make 1000 offers after filtering 42000 offers
> round 42 allocate() took 273.529747ms to make 1000 offers after filtering 43000 offers
> round 43 allocate() took 315.08445ms to make 1000 offers after filtering 44000 offers
> round 44 allocate() took 354.758003ms to make 1000 offers after filtering 45000 offers
> round 45 allocate() took 350.378463ms to make 1000 offers after filtering 46000 offers
> round 46 allocate() took 415.070355ms to make 1000 offers after filtering 47000 offers
> round 47 allocate() took 519.922944ms to make 1000 offers after filtering 48000 offers
> round 48 allocate() took 710.598546ms to make 1000 offers after filtering 49000 offers
> round 49 allocate() took 1.267395251secs to make 0 offers after filtering 50000 offers
> round 50 allocate() took 1.210188235secs to make 0 offers after filtering 50000 offers
> 
> 
> Thanks,
> 
> Meng Zhu
> 
>


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