On Thu, Nov 19, 2020 at 07:34:13PM +0100, Thomas Gleixner wrote: > On Thu, Nov 19 2020 at 13:18, Frederic Weisbecker wrote: > > On Fri, Nov 13, 2020 at 03:02:19PM +0100, Thomas Gleixner wrote: > >> RT requires the softirq to be preemptible and uses a per CPU local lock to > >> protect BH disabled sections and softirq processing. Therefore RT cannot > >> use the preempt counter to keep track of BH disabled/serving. > >> > >> Add a RT only counter to task struct and adjust the relevant macros in > >> preempt.h. > > > > You may want to describe a bit the reason for this per task counter. > > It's not intuitive at this stage. > > Something like this: > > RT requires the softirq processing and local bottomhalf disabled regions > to be preemptible. Using the normal preempt count based serialization is > therefore not possible because this implicitely disables preemption. > > RT kernels use a per CPU local lock to serialize bottomhalfs. As > local_bh_disable() can nest the lock can only be acquired on the > outermost invocation of local_bh_disable() and released when the nest > count becomes zero. Tasks which hold the local lock can be preempted so > its required to keep track of the nest count per task. > > Add a RT only counter to task struct and adjust the relevant macros in > preempt.h. > > Thanks, Very good, thanks!
