在 2019/12/2 18:06, Paolo Bonzini 写道: > On 02/12/19 10:42, Longpeng (Mike) wrote: >>> cond_resched in vfio_iommu_map. Perhaps you could add one to >>> vfio_pin_pages_remote and/or use vfio_pgsize_bitmap to cap the >>> number of pages that it returns. >> Um ... There's only one running task (qemu-kvm of the VM1) on that >> CPU, so maybe the cond_resched() is ineffective ? > > Note that synchronize_sched() these days is just a synonym of > synchronize_rcu, so this makes me wonder if you're running on an older > kernel and whether you are missing this commit: > Yep. I'm running on an older kernel and I've missed this patchset. Thanks a lot :) > > commit 92aa39e9dc77481b90cbef25e547d66cab901496 > Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > Date: Mon Jul 9 13:47:30 2018 -0700 > > rcu: Make need_resched() respond to urgent RCU-QS needs > > The per-CPU rcu_dynticks.rcu_urgent_qs variable communicates an urgent > need for an RCU quiescent state from the force-quiescent-state > processing > within the grace-period kthread to context switches and to > cond_resched(). > Unfortunately, such urgent needs are not communicated to need_resched(), > which is sometimes used to decide when to invoke cond_resched(), for > but one example, within the KVM vcpu_run() function. As of v4.15, this > can result in synchronize_sched() being delayed by up to ten seconds, > which can be problematic, to say nothing of annoying. > > This commit therefore checks rcu_dynticks.rcu_urgent_qs from within > rcu_check_callbacks(), which is invoked from the scheduling-clock > interrupt handler. If the current task is not an idle task and is > not executing in usermode, a context switch is forced, and either way, > the rcu_dynticks.rcu_urgent_qs variable is set to false. If the current > task is an idle task, then RCU's dyntick-idle code will detect the > quiescent state, so no further action is required. Similarly, if the > task is executing in usermode, other code in rcu_check_callbacks() and > its called functions will report the corresponding quiescent state. > > Reported-by: Marius Hillenbrand <mhillenb@xxxxxxxxx> > Reported-by: David Woodhouse <dwmw2@xxxxxxxxxxxxx> > Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > > Thanks, > > Paolo > > > . > -- Regards, Longpeng(Mike)
