Re: [Boost-users] what can you get from boost::thread?

From: Anthony Williams (anthony.ajw_at_[hidden])
Date: 2008-05-27 17:12:31

Kim Kuen tang <kuentang_at_[hidden]> writes:

> i've written a small code for estimating the mean from a series of 
> random numbers.
> The random numbers are generated with and without boost::thread.
>
> The simulation shows me that with boost::thread you only get a small 
> performance.

The problem is not with boost::thread, but with false sharing. The
results[] array is all in a single cache line, so that cache line has
to bounce between the threads with each write.

If you change the SimClass operator() to operate on a local variable
and then store the final result in data_ you should get a much better
performance improvement.

> So my question is, how much performance can you get for simulation with 
> boost::thread?

If you've got too many threads, and too much synchronization or false
sharing, then you can get a performance drop. If you do things right,
you can get almost an N* performance gain, where N is the number of
hardware threads in your machine (typically num cores per processor *
num processors)

Anthony
-- 
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