Mail Archives: cygwin/2003/03/28/19:13:35
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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