Wireshark · Ethereal-dev: Re: [Ethereal-dev] Re: [Ethereal-cvs] rev 16615: /trunk/image/: Makefile.nmake dumpcap.rc.in /trunk/

["Mark H. Wood" <mwood@xxxxxxxxx>]

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On Mon, 28 Nov 2005, Guy Harris wrote:
> Richard Sharpe wrote:
> > What he means is that a modern UNIX/Linux system shares all the pages,
> > so the fact that you run the same program twice does not cost you much.
> > And, with Copy on Write, even pages that are modified in each of the
> > images don't cost much.
> >
> > I suspect that Windows does as well.
>
> You're probably right.
>
> However, a fork (which would be done on UN*X) involves setting all the
> data pages to copy-on-write, which can be somewhat expensive (marking
> them non-writeable in the MMU, etc.), and the exec (done on both
> platforms) might involve faulting in the relevant pages, even if it's a
> minor fault (satisfied by finding the page in the page pool), so
> launching the executable might not be cheap (even if it's cheaper on
> UN*X than on Windows).

You should see the painfully long startup time for captures on a P/166 MMX
64MB box I have.  It takes a long time for the UI to assemble itself, and
that I expect.  But starting the capture takes nearly as long all over
again, and that I do *not* expect.  95% of the code in that subprocess
will never be touched, but it seems to make things slow anyway.

Okay, this box is old and small.  But some current embedded systems don't
have much memory and don't need a lot of CPU horsepower for their usual
tasks.  I suspect that a minimal capture program would be very welcome
on such hosts, and it wouldn't be unwelcome anywhere else.

- -- 
Mark H. Wood, Lead System Programmer   mwood@xxxxxxxxx
Open-source executable:  $0.00.  Source:  $0.00  Control:  priceless!

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