On Wed, 23 Sep 2020 10:40:32 +0200 peterz@xxxxxxxxxxxxx wrote: > However, with migrate_disable() we can have each task preempted in a > migrate_disable() region, worse we can stack them all on the _same_ CPU > (super ridiculous odds, sure). And then we end up only able to run one > task, with the rest of the CPUs picking their nose. What if we just made migrate_disable() a local_lock() available for !RT? I mean make it a priority inheritance PER CPU lock. That is, no two tasks could do a migrate_disable() on the same CPU? If one task does a migrate_disable() and then gets preempted and the preempting task does a migrate_disable() on the same CPU, it will block and wait for the first task to do a migrate_enable(). No two tasks on the same CPU could enter the migrate_disable() section simultaneously, just like no two tasks could enter a preempt_disable() section. In essence, we just allow local_lock() to be used for both RT and !RT. Perhaps make migrate_disable() an anonymous local_lock()? This should lower the SHC in theory, if you can't have stacked migrate disables on the same CPU. -- Steve
