On Wed, Jan 20, 2016 at 04:11:14PM +0100, Thomas Gleixner wrote: > On Wed, 20 Jan 2016, Frederic Weisbecker wrote: > > On Wed, Jan 20, 2016 at 10:09:06AM +0100, Peter Zijlstra wrote: > > > Also, since when can we have enqueues/dequeues while NOHZ_FULL ? I > > > thought that was the 1 task 100% cpu case, there are no > > > enqueues/dequeues there. > > > > That's the most optimized case but we can definetly have small moments with > > more than one task running. For example if we have a workqueue, or such > > short and quick tasks. > > > > If the user makes use of full dynticks for soft isolation (for performance, > > can live with a few interrupts...), there can be short moments of > > multitasking. > > Again, you are trying to make the second step after the first one is > completed. We do not even have proper accounting when we have the ONE task > 100% case and still you try to solve problems beyond that. > > If that ONE task gets interrupted, then accounting should take place. > > When there is another runnable task then that nohz state needs to be left. You > can go back to it once the task is alone again. > > You are trying to make the complete accounting 'almost' tick independent, but > approaching that from the tick nohz angle is wrong. > > When you really want to go there, and I can see why you want that, then you > need to solve this from ground up and such a solution has nothing to do with > any flavour of NOHZ. That simply needs to rework the whole accounting > machinery and rip out the complete tick dependency. Once you have that your > NOHZ business falls into place. Any other approach is just duct tape > engineering.
Alright, let me respawn that series with handling the most simple and common scenario, which is 100% single task in full dynticks, and anything else keeps the tick. That will indeed allow us a more incremental approach. Thanks.
