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

From: Waiman Long
Date: Wed Aug 24 2016 - 14:40:19 EST

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.


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.