Messages in this thread Patch in this message | | | Date | Wed, 06 Jul 2016 18:05:58 +0800 | From | xinhui <> | Subject | Re: [PATCH v2 0/4] implement vcpu preempted check |
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On 2016年07月06日 14:52, Peter Zijlstra wrote: > On Tue, Jun 28, 2016 at 10:43:07AM -0400, Pan Xinhui wrote: >> change fomr v1: >> a simplier definition of default vcpu_is_preempted >> skip mahcine type check on ppc, and add config. remove dedicated macro. >> add one patch to drop overload of rwsem_spin_on_owner and mutex_spin_on_owner. >> add more comments >> thanks boqun and Peter's suggestion. >> >> This patch set aims to fix lock holder preemption issues. >> >> test-case: >> perf record -a perf bench sched messaging -g 400 -p && perf report >> >> 18.09% sched-messaging [kernel.vmlinux] [k] osq_lock >> 12.28% sched-messaging [kernel.vmlinux] [k] rwsem_spin_on_owner >> 5.27% sched-messaging [kernel.vmlinux] [k] mutex_unlock >> 3.89% sched-messaging [kernel.vmlinux] [k] wait_consider_task >> 3.64% sched-messaging [kernel.vmlinux] [k] _raw_write_lock_irq >> 3.41% sched-messaging [kernel.vmlinux] [k] mutex_spin_on_owner.is >> 2.49% sched-messaging [kernel.vmlinux] [k] system_call >> >> We introduce interface bool vcpu_is_preempted(int cpu) and use it in some spin >> loops of osq_lock, rwsem_spin_on_owner and mutex_spin_on_owner. >> These spin_on_onwer variant also cause rcu stall before we apply this patch set >> > > Paolo, could you help out with an (x86) KVM interface for this? > > Waiman, could you see if you can utilize this to get rid of the > SPIN_THRESHOLD in qspinlock_paravirt? > hmm. maybe something like below. wait_node can go into pv_wait() earlier as soon as the prev cpu is preempted. but for the wait_head, as qspinlock does not record the lock_holder correctly(thanks to lock stealing), vcpu preemption check might get wrong results.
Waiman, I have used one hash table to keep the lock holder in my ppc implementation patch. I think we could do something similar in generic code?
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h index 74c4a86..40560e8 100644 --- a/kernel/locking/qspinlock_paravirt.h +++ b/kernel/locking/qspinlock_paravirt.h @@ -312,7 +312,8 @@ pv_wait_early(struct pv_node *prev, int loop) if ((loop & PV_PREV_CHECK_MASK) != 0) return false; - return READ_ONCE(prev->state) != vcpu_running; + return READ_ONCE(prev->state) != vcpu_running || + vcpu_is_preempted(prev->cpu); } /*
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