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Date: Wed, 5 Aug 2015 15:34:43 +0200
From: Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH 3/5] KVM: add KVM_USER_EXIT vm ioctl for userspace exit
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2015-08-05 15:29+0200, Paolo Bonzini:
> On 05/08/2015 15:21, Radim Krčmář wrote:
>> +	kvm_for_each_vcpu(idx, vcpu, kvm)
>> +		if (vcpu->vcpu_id == vcpu_id) {
>> +			kvm_make_request(KVM_REQ_EXIT, vcpu);
>> +			kvm_vcpu_kick(vcpu);
>> +
>> +			return 0;
>> +		}
>> +
> 
> Why not a vcpu ioctl?  kvm_for_each_vcpu can become pretty expensive if
> you have a few dozen VCPUs.

Yeah, it will be slow, the only bright side is low frequency of calls.

vcpu ioctl should only be issued by the vcpu thread so it would
significantly limit use.