> hm, then why does causal.c trigger a causality violation on a 8-way box?
> Interestingly it's getting triggered if there are two copies (4 threads
> total) running. [which could be simply just randomness added to the system
> bus load and thus statistically finds the window]
[snip]
> note that this cannot be reproduced on Andrea's dual-PII box (neither on
> my dual-PIII box), but can be reproduced on my 8-way Xeon box, if two
> copies of the above are running. [maybe if i added delay timings to the
> above then we could trigger it on dual boxes too] 'two copies' means two
> independent pairs of the above.
I got something like this:
<1943260> 7223479 996367527
<thread1> BROKE causality! Weakly ordered memory?
<15802145> 12115409 998555500
<thread1> BROKE causality! Weakly ordered memory?
<3699222> 4779261 999405279
<thread1> BROKE causality! Weakly ordered memory?
I was running a handful 'causal' and I was doing other stuff as well at
the same time. (The reason for running so many was that I didn't really
check what it did, so I started a few thinking that they had completed
without finding anything ...
history:
3 20:17 t causal.c
4 20:17 gcc -O2 -o causal causal.c
"normal compile"
5 20:18 ./causal 0 2
6 20:18 ./causal 0 2
7 20:18 ./causal 0 2
8 20:18 ./causal 0 2
9 20:18 ./causal 0 2
10 20:18 ./causal 0 2
11 20:18 ./causal 0 2
12 20:18 ./causal 0 2
13 20:18 ./causal 0 2
14 20:18 ./causal 1 2
15 20:18 ./causal 1 2
16 20:18 ./causal 1 2
17 20:18 ./causal 1 2
18 20:18 gcc -o causal causal.c
"maybe it was the -O2 ?"
19 20:18 ./causal 0 2
20 20:18 ./causal 0 2
21 20:18 ./causal 0 2
22 20:18 ./causal 0 2
23 20:18 ./causal 0 2
24 20:18 ./causal 0 2
25 20:18 ./causal 0 2
26 20:18 ./causal 1 2
"still nothing fun happens ..."
27 20:18 t causal.c
28 20:19 t causal.c
"read, but not understood"
29 20:21 rm causal*
"remove some junk"
30 20:31 killall causal
"hmm, system is much less responsive than normal ... oh, they were
all still running"
)
This on a dual PIII-500.
/Urban
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