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Date:	Tue, 26 Feb 2013 06:22:40 -0500
From:	"Chris J. Breisch" <chris DOT ml AT breisch DOT org>
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To:	cygwin AT cygwin DOT com
Subject:	Re: wrong performance of malloc/free under multi-threading
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On 2/26/2013 4:14 AM, Corinna Vinschen wrote:
> On Feb 26 15:35, MITSUNARI Shigeo wrote:
>> Hi.
>>
>> I found that the performance of malloc/free is wrong under multi-threading.
>> The following test program reproduces the problem.
>>
>> The program repeats malloc and free under multi-thread.
>> I measured the timing on Cygwin and Linux.
>>
>> timing(sec)|      threadNum
>> -----------+----------+-------------
>>             | 1        |     2
>> -----------+----------+-------------
>> Linux      | 1.45     |     0.69
>> -----------+----------+-------------
>> Cygwin     | 2.059    |    53.165
>> -----------+----------+-------------
>>
>> The timing under Linux seems good scale but it is very wrong under Cygwin.
>> Is it intentional behavior or do I use pthread in bad way?
>
> No, you're right.  This is easily reproducable.  I just had a look and
> it seems that our malloc is really slow in multi-threading scenarios.
> We're using Doug Lea's malloc unchanged with just additional locks
> surrounding the underlying malloc/free calls.
>
> This appears to be a serious performance problem.  I just learned that
> glibc uses another version of dlmalloc, called ptmalloc, which is a
> derived version of dlmalloc optimized for multi-threading environments.
>
> Perhaps we have to do the same, but I don't know how long it takes to
> port ptmalloc to Cygwin and obviously I don't know how big the
> performance gain might be.
>
>
> Corinna
>

Does any host using newlib suffer from this problem, or is it exclusive 
to Cygwin?

Chris

-- 
In theory, there's no difference between theory and practice. In 
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