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

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@xxxxxxxx>
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).


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