linux-kernel - Re: [PATCH 3/3] KVM: make make_all_cpus

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Message-ID: <4D243FEF.6090105@redhat.com>
Date:	Wed, 05 Jan 2011 11:54:55 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 3/3] KVM: make make_all_cpus_request() lockless

On 01/05/2011 11:40 AM, Xiao Guangrong wrote:
> Now, we have 'vcpu->guest_mode' to judge whether need to send
> ipi to other cpus, this way is very exact, so checking request
> bit is needless, then we can drop the spinlock let it's collateral

Clever.

> @@ -147,11 +147,9 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
>
>   	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
>
> -	raw_spin_lock(&kvm->requests_lock);
> -	me = smp_processor_id();
> +	me = get_cpu();
>   	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		if (kvm_make_check_request(req, vcpu))
> -			continue;
> +		kvm_make_request(req, vcpu);
>   		cpu = vcpu->cpu;
>   		if (cpus != NULL&&  cpu != -1&&  cpu != me&&
>   		atomic_read(&vcpu->guest_mode))
> @@ -163,7 +161,7 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
>   		smp_call_function_many(cpus, ack_flush, NULL, 1);
>   	else
>   		called = false;
> -	raw_spin_unlock(&kvm->requests_lock);
> +	put_cpu();
>   	free_cpumask_var(cpus);
>   	return called;
>   }

Maybe we can drop 'cpu != me' and then we don't need to disable preemption?

Can be done in a later patch.

Anyway, I really like this, requests_lock is an ugly wart.

-- 
error compiling committee.c: too many arguments to function

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