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Re: cygwin fork()
On Fri, 1 Sep 2006, clayne wrote:
> On Fri, Sep 01, 2006 at 11:12:59AM +0100, Dave Korn wrote:
> > On 01 September 2006 11:02, clayne@anodized.PCYMTNQREAIYA wrote:
> >
> > > Is it just me or is cygwin fork(), or a support syscall underneath,
> > > terribly slow for some reason?
> >
> > Some reason == "lack of O/S support".
>
> Basically, this is what I'm talking about:
>
> Opteron 180, fast disks, ran make clean, make 4 times or so to keep the
> disk/mem/cpu caches hot; no extraneous system usage going on:
>
> $ ( make clean; time make -j1 ; make clean; time make -j8 ) >/dev/null
>
> real 2m20.062s
> user 0m13.252s
> sys 0m37.139s
>
> real 0m45.654s
> user 0m15.968s
> sys 0m49.201s
>
> That's a huge difference, and it's only like 6300 lines of code! I've
> narrowed it down to something between 20060309 and 20060313 snapshots. Every
> snapshot since 20060313 has had this incredible slowness issue with fork().
>
> The dual-coreness isn't going to make a huge difference here as I can get
> the same factor of speed up just by using 20060309's dll and the exact
> same make jobs. Nor is it a case of minor differences in times. I've tried
> different versions of libtool, gcc, etc. Everything just goes back to
> 20060309 vs 20060313.
Ok, but now you're in a perfect position to debug this further. There
were only 6 sets of changes between those two snapshots (see the
cygwin-cvs archives). If you can build Cygwin as of those times and
pinpoint the change that made the difference, that in itself would
probably be helpful in diagnosing the problem.
Igor
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