Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR

Waiman Long
2020-07-23T19:04:22Z

On 7/23/20 2:47 PM, peterz@infradead.org wrote:
> On Thu, Jul 23, 2020 at 02:32:36PM -0400, Waiman Long wrote:
>> BTW, do you have any comment on my v2 lock holder cpu info qspinlock patch?
>> I will have to update the patch to fix the reported 0-day test problem, but
>> I want to collect other feedback before sending out v3.
> I want to say I hate it all, it adds instructions to a path we spend an
> aweful lot of time optimizing without really getting anything back for
> it.

It does add some extra instruction that may slow it down slightly, but I
don't agree that it gives nothing back. The cpu lock holder information
can be useful in analyzing crash dumps and in some debugging situation.
I think it can be useful in RHEL for this readon. How about an x86
config option to allow distros to decide if they want to have it
enabled? I will make sure that it will have no performance degradation
if the option is not enabled.

Cheers,
Longman