Re: [Xen-devel] [PATCH v2] xen/sched: add some diagnostic info in the run queue keyhandler

["Jürgen Groß" <jgross@suse.com>]

On 11.02.20 14:01, Jan Beulich wrote:
> On 11.02.2020 13:27, Juergen Gross wrote:
>> When dumping the run queue information add some more data regarding
>> current and (if known) previous vcpu for each physical cpu.
>>
>> With core scheduling activated the printed data will be e.g.:
>>
>> (XEN) CPUs info:
>> (XEN) CPU[00] current=d[IDLE]v0, curr=d[IDLE]v0, prev=NULL
>> (XEN) CPU[01] current=d[IDLE]v1
>> (XEN) CPU[02] current=d[IDLE]v2, curr=d[IDLE]v2, prev=NULL
>> (XEN) CPU[03] current=d[IDLE]v3
>>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> V2: add proper locking
> 
> "Proper" is ambiguous in the context of dumping functions. In a
> number of places we use try-lock, to avoid the dumping hanging
> on something else monopolizing the lock. I'd like to suggest to
> do so here, too.

All the scheduler related dumping functions are using the "real" locks.
So using trylock in this single case wouldn't help at all. Additionally
using trylock only would make a crash during dumping the data more
probable, so I'm not sure we want that.

Instead of unconditionally using trylock in dumping functions I could
imagine to have a "dumplock" using proper locking by default which can
be toggled to trylock in case it is needed (or maybe automatically by
adding a timeout to the dumplock variant).


Juergen

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