Re: KDB improvements for IA64

[Francois Wellenreiter <Francois.Wellenreiter@bull.net>]

>>>>>>On Tue, 10 May 2005 17:27:01 +0200, Francois Wellenreiter <Francois.Wellenreiter@bull.net> said:
> 
> 
>   Francois> - timeouts when exiting from KDB will never occur I have
>   Francois> noticed that after a long time in KDB, some drivers enter
>   Francois> in timeout sequences. Now, the different ITC values are
>   Francois> saved when entering KDB and restored when going out.
> 
> This sounds fragile to me.  For one thing, the kernel may not use ITC
> at all for timeouts (true for most NUMA platforms).  Also, even if the
> ITC is in use, you'd probably have to resync them on the slave CPUs
> after restoring the time-keeper's ITC value.  Not to mention that if
> the timeout is related to an external event, then faking time won't
> help no matter what.
> 
> 	--david
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		David,

	I agree that ITC management may be a bit risky and overall is 
platform-dependent, but in my opinion, that was a better way than saving and
restoring global xtime variable which can be modified by only one CPU
(the main danger in such a case may occur when this CPU is working
when the other ones are already running KDB).

The time-outs that I have noticed dealt with journalled filesystem messages
(and sometimes lead to an unrecoverable machine crash),
that is the reason why I have implemented this feature. On the different
NUMA machines that I have tested, this problem did not appear again.

If you have some implementation ideas, they are really welcome.

Regards,

		Francois