Re: [Xen-devel] [FIXED] time still going backwards

[Tim Freeman <tfreeman@xxxxxxxxxxx>]

The time going backwards is no longer a problem.  I believe it was
particular benchmarks that required too many big messages which maxed
out the RAM.  The masters had no swapspace and it bombed on that, now
they don't.  I feel dumb that it took five runs before I tried adding
swap as the EOF is a big clue.

I posted the PMB MPI results here (no interpretation):
http://www-unix.mcs.anl.gov/~tfreeman/envelope/index.html

This is only a preliminary "back of the envelope" set of runs that I
only had time to think about off and on this week.  This isn't part of
my globus-VM project, it was just a "see what happens" experiment since
Xen was installed anyhow.  I have no time left for it but there they
are, whatever they're worth.

I do have some thoughts on the runs in Part I.  In general, the raw and
Xen results converged as the message size got bigger.  This is most
likely due to the fact that domain0 needs to bridge guests' packets.  As
they got bigger, more could be moved at once and so was faster out the
box per byte.  Right? 



btw, for reference, before trying the swap idea, I tried moving the
masters to a new physical node, it bombed, and the XenU's reported a new
error:

__alloc_pages: 0-order allocation failed (gfp=0x1d2/0) 
VM: killing process PMB-MPI1


And that run, the time only went backwards on Xen0. 

I didn't add the struct to the debug, it wouldn't compile and I was too
much in a rush to figure out the intended extra arg, sorry. 

printk("Timer ISR: Time went backwards: %lld %lld %lld\n", delta,
shadow_system_time, processed_system_time);

Xen0, just two again:
Timer ISR: Time went backwards: -59842000 7226230000000 7226290000000
Timer ISR: Time went backwards: -49988000 7226240000000 7226290000000



Thanks for the help before!  I really appreciate it, but my fault here
-- but these errors are strange still, aren't they?










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