Message-ID: <45804D3A.6060602@algonet.se>
Date: Wed, 13 Dec 2006 19:58:02 +0100
From: Magnus Holmgren <lear AT algonet DOT se>
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Subject: Cygwin slower on one computer
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Hi,

I'm trying to figure out why Cygwin build things so much slower on one 
computer I have. We're talking about more than 3 times slower on a 
computer that ought to be a bit faster (Athlon64 at 2.2-2.4 GHz, 
compared to a  Pentium M at 1.8 GHz).

After digging into strace logs a bit, it seems like the Athlon is a bit 
faster at first, but after a while (after creating a bunch of child 
processes?), things change, making it a bit slower. Mostly not too much, 
around 10-20% or so, but sometimes about 100%. And there's one step 
where this could make things really bad. During startup of a program, 
lines like the following are displayed (some whitespace editing done):

    59      294 [main] make 2936 child_copy: dll data -
                hp 0x6BC low 0x61100000, high 0x61104BA0, res 1
157457  157751 [main] make 2936 child_copy: dll bss -
                hp 0x6BC low 0x6113F000, high 0x611483E0, res 1
   205   157956 [main] make 2936 child_copy: user heap -
                hp 0x6BC low 0x680000, high 0x6A0000, res 1
    25   157981 [main] make 2936 child_copy: done

Now, that "dll bss" copy time fluctuates quite a bit, so in one case 
(from the Athlon computer) the time is 32146275... (It might be worth 
mentioning that the log in question is some 35 MB. Maybe that can throw 
the timing off a bit?)

Any ideas what could cause this slowdown? Could the child_copy part be 
involved? Since it involves the Win32 functions 
ReadProcessMemory/WriteProcessMemory, I imagine it could impact 
performance noticeably, in unpredictable ways (since it would need to 
mess around with memory protection stuff).

One thing that suggests something strange is going on is the fact that 
if I have a background process running (like Folding AT Home (which doesn't 
affect the build time, btw)), the CPU load drops noticably (according to 
Process Explorer), from 100% to something like 75-85%.

I've tried disabling anti-virus, firewalls, background processes and the 
like, but it has little to no impact on the build times.

   Magnus

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