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Date: Sat, 28 May 2005 15:02:26 -0400
From: Christopher Faylor <cgf-no-personal-reply-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Serious performance problems (Gerrit/Danny please comment)
Message-ID: <20050528190226.GA3094@trixie.casa.cgf.cx>
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References: <4297A14B DOT 9070409 AT plausible DOT org> <20050528131501 DOT V53507 AT logout DOT sh DOT cvut DOT cz> <20050528185720 DOT GA3015 AT trixie DOT casa DOT cgf DOT cx>
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On Sat, May 28, 2005 at 02:57:20PM -0400, Christopher Faylor wrote:
>On Sat, May 28, 2005 at 01:24:31PM +0200, Vaclav Haisman wrote:
>>Somebody mentioned that malloc implementation could be the problem.
>>Dunno.  I has also crossed my mind that another difference between
>>FreeBSD and Cygwin is implementation of C++ exceptions.  Maybe the SJLJ
>>implementation that Cygwin AFAIK uses has too big overhead.
>
>To test this theory, I just tried replacing Cygwin's "Unwind" functions
>with those from mingw and saw a noticeable speed up in the execution of
>this program.  I did this by extracting the contents of mingw's libgcc
>to a directory and then including unwind-c.o and unwind-sjlj.o on the
>command line when linking the test case.  I had to modify the test case
>by adding these two lines to the bottom:
>
>int __mingwthr_key_dtor; int _CRT_MT;
>
>to avoid undefined symbol errors so this is obviously not intended as a
>complete solution.
>
>On doing this, the program went from taking 25 seconds to execute to
>taking 7 seconds to execute.  That's still 4x slower than mingw but it
>is, nonetheless, a noticeable difference.
>
>Gerrit and Danny do you know what the difference between the mingw and
>cygwin implementations of these functions might be?

Two things that I meant to add:

- In case it isn't clear, Vaclav's theory is very plausible.

- The malloc implementation in Cygwin is Doug Lea's famous malloc
implementation.  The locking of malloc should be, in the absence of
thread contention, accomplished by a the use of a fast
InterlockedIncrement/InterlockedDecrement so, even if malloc was
being called in this loop (which it isn't), this should not provide
excessive overhead.

cgf

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