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Date: Fri, 28 Mar 2003 19:13:48 -0500
From: Christopher Faylor <cgf AT redhat DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Mozilla 1.3 built on cygwin?
Message-ID: <20030329001348.GA1533@redhat.com>
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References: <20030328234857 DOT GA971 AT redhat DOT com> <LPEHIHGCJOAIPFLADJAHKEKFDHAA DOT chris AT atomice DOT net>
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On Sat, Mar 29, 2003 at 12:04:01AM -0000, Chris January wrote:
>> On Thu, Mar 27, 2003 at 11:58:50PM +0100, Ralf Habacker wrote:
>>>I can't prove a fact, that forking is the most anonying problem and
>>>there were some initial work from some people (I remember Chris Faylor,
>>>Chris January and other) to identify the problems and to implement a
>>>new copy-on-write semantic, which will be much faster,
>>
>>You misremember.  I did hobble together a copy-on-write implementation
>>and found that it was actually slower.  The generic win32
>>implementation of copy-on-write isn't powerful enough to completely
>>implement fork anyway.
>
>Noone has explained, however, *why* the copy-on-write implementation
>was slower.  Perhaps we have just been using the wrong tests.  Does
>copy-on-write actually perform slower in "real world" tests?  I don't
>know, because I only used the skeleton example found in Nebbit's book.

I implemented it with both the win32 api and with the skeleton example.
Neither was a speed daemon.  I can't think of a better test than doing a
bunch of forks and measuring the results.  Who knows why it is slower?
Maybe ReadProcessMemory is doing copy-on-write already or something.

When I first started with Cygnus, my first order of business for cygwin
was going to be implementing copy-on-write for fork.  I had something
almost working but it was not an improvement.  It was disappointing.
So, after a couple of weeks of poking, I abandoned the approach.  I
revisited things later after reading the Nebbit book.  Similar results.

Note to present and future readers of this message: Please don't contact
me to ask what I did or try to compare notes with me.  It seems like
every time I mention this, I get an enthusiastic message from someone
six months later who's gung ho to get copy-on-write working and is
certain that I'd love to begin a long email dialog about how it could
all be done.

I don't have the code anymore and, while I will certainly review any
cygwin improvements, I'm not interested in mentoring someone through
the process.  I couldn't do that anyway since the knowledge has been
swapped out for some time.

cgf
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