Re: [RFC PATCH-tip v4 10/10] locking/rwsem: Add a boot parameter to reader spinning threshold

Waiman Long
2016-08-24T18:39:11Z

On 08/24/2016 12:00 AM, Davidlohr Bueso wrote:
> On Thu, 18 Aug 2016, Waiman Long wrote:
>
>> The default reader spining threshold is current set to 4096. However,
>> the right reader spinning threshold may vary from one system to
>> another and among the different architectures. This patch adds a new
>> kernel boot parameter to modify the threshold value. This enables
>> better tailoring to the needs of different systems as well as for
>> testing purposes.
>
> It also means that those systems could very easily be incorrectly
> tailored.
> (and worse case scenario: reboot, is obviously a terrible way to get rid
> of any issues). I very much disagree with exposing this sort of core
> stuff,
> it should work well for everyone out of the box, not relying on users to
> properly configure this.
>
> Thanks,
> Davidlohr

I also have some concern about exposing this kernel parameter as it will
be hard to tune. That is why I put it at the end to gauge the opinion of
others. I will leave this out when I send out the next version.

Cheers,
Longman