Re: [Boost-bugs] [Boost C++ Libraries] #9282: performance regression in boost::unordered on 64-bit platforms

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #9282: performance regression in boost::unordered on 64-bit platforms
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-10-23 22:26:44

#9282: performance regression in boost::unordered on 64-bit platforms
--------------------------+------------------------------------------------
  Reporter:  aiapub-      |      Owner:  danieljames
  cpp@…                   |     Status:  assigned
      Type:  Bugs         |  Component:  unordered
 Milestone:  To Be        |   Severity:  Regression
  Determined              |   Keywords:  unordered mix64_policy performance
   Version:  Boost        |
  1.53.0                  |
Resolution:               |
--------------------------+------------------------------------------------

Comment (by danieljames):

 It just occurred to me that my old laptop is running a 64 bit operating
 system. It only has 2 GB memory, so I couldn't run it for as many records.
 I ran it for 30M records and I got the kind of distribution I'd expect.

 But the performance was worse than I expected (about twice as long for the
 mix policy). I'm not sure, but I think it might be because of bad cache
 coherency. The mix policy is jumping around the buckets array, while the
 prime policy is moving through it linearly. So even if there's an empty
 bucket the mix policy is much more likely to have a cache miss when
 checking the bucket. I'll think about this.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9282#comment:5>
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