Re: [Xen-devel] [PATCH 3/7] xen: rework locking for dump of scheduler info (debug-key r)

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.03.15 at 12:05, <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 03/17/2015 10:54 AM, Jan Beulich wrote:
>> Finally, as said in different contexts earlier, I think unconditionally
>> acquiring locks in dumping routines isn't the best practice. At least
>> in non-debug builds I think these should be try-locks only, skipping
>> the dumping when a lock is busy.
> 
> You mean so that we don't block the console if there turns out to be a
> deadlock?

For example. And also to not unduly get in the way of an otherwise
extremely busy system.

> That makes some sense; but on a busy system that would mean a
> non-negligible chance that any give keystroke would be missing
> information about some cpu or other, which would be pretty frustrating
> for someone trying to figure out the state of their system.

Right - ideally there would be an indication of the skipped state
left in the log.

> Would it make sense to have a version of spin_trylock for use in this
> kind of situation that waits & retries a reasonable number of times
> before giving up?

Yes, that might be a possible compromise. I could also imagine
another debug key allowing to alter the behavior, i.e. for when
one absolutely wants the information and doesn't care about
the state of the system.

Jan


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