Messages in this thread | | | Date | Wed, 4 Jan 2017 13:49:29 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH 0/7] locking/rtqspinlock: Realtime queued spinlocks |
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On Tue, Jan 03, 2017 at 01:00:23PM -0500, Waiman Long wrote: > This patchset introduces a new variant of queued spinlocks - the > realtime queued spinlocks. The purpose of this new variant is to > support real spinlock in a realtime environment where high priority > RT tasks should be allowed to complete its work ASAP. This means as > little waiting time for spinlocks as possible. > > Non-RT tasks will wait for spinlocks in the MCS waiting queue as > usual. RT tasks and interrupts will spin directly on the spinlocks > and use the priority value in the pending byte to arbitrate who get > the lock first. > > Patch 1 removes the unused spin_lock_bh_nested() API. > > Patch 2 introduces the basic realtime queued spinlocks where the > pending byte is used for storing the priority of the highest priority > RT task that is waiting on the spinlock. All the RT tasks will spin > directly on the spinlock instead of waiting in the queue. >
OK, so a single numerical field isn't sufficient to describe priority anymore, since we added DEADLINE support things have gotten a lot more complex.
Also, the whole approach worries me, it has the very real possibility of re-introducing a bunch of starvation cases avoided by the fair lock.
Is there a real problem with -RT that inspired these patches?
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