Messages in this thread | | | Date | Wed, 21 Dec 2005 05:36:41 -0800 | From | "Paul E. McKenney" <> | Subject | Re: 2.6.14-rt22 (and mainline) excessive latency |
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On Tue, Dec 20, 2005 at 10:32:48PM -0500, Lee Revell wrote: > On Tue, 2005-12-20 at 17:47 -0800, Paul E. McKenney wrote: > > On Tue, Dec 20, 2005 at 05:24:42AM +0100, Ingo Molnar wrote: > > > > > > * Lee Revell <rlrevell@joe-job.com> wrote: > > > > > > > I captured this 3+ ms latency trace when killing a process with a few > > > > thousand threads. Can a cond_resched be added to this code path? > > > > > > > bash-17992 0.n.1 29us : eligible_child (do_wait) > > > > > > > > [ 3000+ of these deleted ] > > > > > > > > bash-17992 0.n.1 3296us : eligible_child (do_wait) > > > > > > Atomicity of signal delivery is pretty much a must, so i'm not sure this > > > particular latency can be fixed, short of running PREEMPT_RT. Paul E. > > > McKenney is doing some excellent stuff by RCU-ifying the task lookup and > > > signal code, but i'm not sure whether it could cover do_wait(). > > > > Took a quick break from repeatedly shooting myself in the foot with > > RCU read-side priority boosting (still have a few toes left) to take > > a quick look at this. The TASK_TRACED and TASK_STOPPED cases seem > > non-trivial, and I am concerned about races with exit. > > > > Any thoughts on whether the latency is due to contention on the > > tasklist lock vs. the "goto repeat" in do_wait()? > > It's a UP system so I'd be surprised if there were any contention.
Couldn't there be contention due to preemption of someone holding the tasklist lock?
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