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SubjectRe: [PATCH v3 3/3] KVM: vCPU kick tax cut for running vCPU
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On 20/10/21 12:02, Wanpeng Li wrote:
>> +#ifdef CONFIG_PREEMPT_RCU
>> + /* The cost of rcu_read_lock() is nontrivial for preemptable RCU. */
>> + if (!rcuwait_active(w))
>> + return ret;
>> +#endif
>> +
>> + rcu_read_lock();
>> +
>> task = rcu_dereference(w->task);
>> if (task)
>> ret = wake_up_process(task);
>>
>> (If you don't, rcu_read_lock is essentially preempt_disable() and it
>> should not have a large overhead). You still need the memory barrier
>> though, in order to avoid missed wakeups; shameless plug for my
>> article athttps://lwn.net/Articles/847481/.
> You are right, the cost of rcu_read_lock() for preemptable RCU
> introduces too much overhead, do you want to send a separate patch?

Yes, I'll take care of this. Thanks!

Paolo

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