[External] : Re: [PATCH v14 4/6] locking/qspinlock: Introduce starvation avoidance into CNA
Alex Kogan
alex.kogan at oracle.com
Tue Apr 13 22:01:37 BST 2021
Hi, Andi.
Thanks for your comments!
> On Apr 13, 2021, at 2:03 AM, Andi Kleen <ak at linux.intel.com> wrote:
>
> Alex Kogan <alex.kogan at oracle.com> writes:
>>
>> + numa_spinlock_threshold= [NUMA, PV_OPS]
>> + Set the time threshold in milliseconds for the
>> + number of intra-node lock hand-offs before the
>> + NUMA-aware spinlock is forced to be passed to
>> + a thread on another NUMA node. Valid values
>> + are in the [1..100] range. Smaller values result
>> + in a more fair, but less performant spinlock,
>> + and vice versa. The default value is 10.
>
> ms granularity seems very coarse grained for this. Surely
> at some point of spinning you can afford a ktime_get? But ok.
We are reading time when we are at the head of the (main) queue, but
don’t have the lock yet. Not sure about the latency of ktime_get(), but
anything reasonably fast but not necessarily precise should work.
> Could you turn that into a moduleparm which can be changed at runtime?
> Would be strange to have to reboot just to play with this parameter
Yes, good suggestion, thanks.
> This would also make the code a lot shorter I guess.
So you don’t think we need the command-line parameter, just the module_param?
Regards,
— Alex
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