Re: [BProc] clone support

[Nicholas H. <he...@se...>]

On Tue, 2003-07-01 at 11:05, er...@he... wrote:
> 
> I believe clone works.  Most of the interesting stuff with clone is
> local to the node and BProc doesn't get involved at all.  So, in
> theory, it should be possible to make Java work.

Ok

> 
> I think there are two things which you are likely to have trouble with:
> 
> 1 - Some of the thread group stuff (CLONE_THREAD) may not work.  This
>     stuff has been kind of fluid in the 2.4.x kernels so it seems
>     unlikely that many things use it.

Why does it seem likely that Java uses it then --- friggin' Java!

> 
> 2 - You cannot migrate a multi-threaded task.  Some of the guys at LBL
>     are working on some extensions to VMADump to do handle
>     multi-threaded tasks for some checkpointing work they're doing but
>     none of this has been combined with BProc at this point.  BProc
>     would also have to become aware of these situations.

That would be very cool.

> 
>     Migration will end up creating copies of the program.  Also, on
>     x86, vmadump isn't aware of funky LDT stuff which will also hamper
>     migration.  Note that this doesn't mean you can't bpsh a
>     multi-threaded program.
> 
> The other possible funny bit that you're likely to run into is that
> fork/clone is much slower than normal because it involves the front
> end.  This could lead to new/interesting races or just poor
> performance in apps that create/clean-up threads a lot.
> 
> In terms of what needs to be done, that depends entirely on what
> you're trying to run.  I've done some simple pthreads things on nodes
> w/o problems.  The first place to look is probably strace output of a
> program that fails.  Then try and figure out how what the app is
> seeing differs from what it's expecting.

We have several programs that use pthreads here as well -- and they seem
to run fine ( apart from the sigsuspend issue in 2.4.19 ), it is just
that java seems a bit confused -- I will put together a complete bug
report, and I guess we can go from there.

Nic
-- 
Nicholas Henke
Penguin Herder & Linux Cluster System Programmer
Liniac Project - Univ. of Pennsylvania