Messages in this thread | | | Date | Tue, 27 Sep 2022 11:52:14 -0400 | Subject | Re: locking/rwsem: RT throttling issue due to RT task hogging the cpu | From | Waiman Long <> |
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On 9/27/22 11:30, Mukesh Ojha wrote: > Hi Waiman, > > Thanks for the reply. > > On 9/27/2022 8:56 PM, Waiman Long wrote: >> On 9/27/22 11:25, Waiman Long wrote: >>> >>> On 9/20/22 12:19, Mukesh Ojha wrote: >>>> Hi, >>>> >>>> We are observing one issue where, sem->owner is not set and >>>> sem->count=6 [1] which means both RWSEM_FLAG_WAITERS and >>>> RWSEM_FLAG_HANDOFF bits are set. And if unfold the sem->wait_list >>>> we see the following order of process waiting [2] where [a] is >>>> waiting for write, while [b],[c] are waiting for read and [d] is >>>> the RT task for which waiter.handoff_set=true and it is >>>> continuously running on cpu7 and not letting the first write waiter >>>> [a] on cpu7. >>>> >>>> [1] >>>> >>>> sem = 0xFFFFFFD57DDC6680 -> ( >>>> count = (counter = 6), >>>> owner = (counter = 0), >>>> >>>> [2] >>>> >>>> [a] kworker/7:0 pid: 32516 ==> [b] iptables-restor pid: 18625 ==> >>>> [c]HwBinder:1544_3 pid: 2024 ==> [d] RenderEngine pid: 2032 cpu: 7 >>>> prio:97 (RT task) >>>> >>>> >>>> Sometime back, Waiman has suggested this which could help in RT task >>>> leaving the cpu. >>>> >>>> https://lore.kernel.org/all/8c33f989-8870-08c6-db12-521de634b34e@redhat.com/ >>>> >>>> >>> Sorry for the late reply. There is now an alternative way of dealing >>> with this RT task hogging issue with the commit 48dfb5d2560d >>> ("locking/rwsem: Disable preemption while trying for rwsem lock"). >>> Could you try it to see if it can address your problem? >> >> FYI, this commit is in the tip tree. It is not in the mainline yet. > > > I only posted that patch so, i am aware about it. In that issue > sem->count was 7 and here it is 6 and current issue occurs after fix > 48dfb5d2560d ("locking/rwsem: Disable preemption while trying for > rwsem lock").
Thanks for the quick reply. So it doesn't completely fix this RT hogging issue. It is harder than I thought. Will look further into this.
Cheers, Longman
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