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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