On 11/25/2014 10:46 AM, Mike Galbraith wrote:
On Tue, 2014-11-25 at 07:50 -0700, Khalid Aziz wrote:
It is definitely not an attempt to solve any kind of RT problem.
No no, I'm saying that giving certain tasks special dispensations
effectively elevates them. Temporarily or otherwise, they play by
different rules, will block more deserving tasks, and it's not cut and
dried that that blocking will not do more harm than good.
Is it a clear win to make say some kworker or other global asset wait
when it could have preempted and been gone in usecs? Nope.
I understand. You are right, this allows some apps to gain special
dispensation. On a general purpose system, I agree this can be
problematic and it is important that it be easy to disable this. This is
why I added sysctl tunable and made "disabled" the default state for
this feature. Allowing temporary elevation of a task as part of the
overall system design is ok when it is intentional and done after
considering impact on other tasks running on the system. A large
database server typically is not a general purpose server that runs any
arbitrary tasks. These systems are tweaked in many ways to ensure
optimal performance for database and not necessarily other apps. This
patch gives admins one more knob to turn when maximizing performance.
Any general purpose system that sees no use for this feature can leave
this feature in its default state of disabled. I can see usefulness of
this patch for other servers used in telecommunication infrastructure
for instance, where the server is dedicated to specific task(s) and
needs to update critical database with minimal contention, for example
switch map on a telco switch controller or channel allocation map on a
base station controller. I am sure people more familiar with other
industries can see usefulness in other dedicated applications.
Thanks,
Khalid
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