linux-kernel - Re: [PATCH v3 2/5] KVM: add KVM_REQ

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Date:	Sat, 22 Aug 2015 00:04:55 -0700
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Wanpeng Li <wanpeng.li@...mail.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org, Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [PATCH v3 2/5] KVM: add KVM_REQ_EXIT request for userspace exit



On 19/08/2015 20:55, Wanpeng Li wrote:
>> The disadvantage is that it adds an overhead of one bit check for all
>> kernel exits.  A quick tracing shows that the ratio of userspace exits
>> after boot is about 1/5 and in subsequent run of nmap and kernel compile
>> has about 1/60, so the check should not regress global performance.
>>
>> All signal_pending() calls are userspace exit requests, so we add a
>> check for KVM_REQ_EXIT there.  There is one omitted call in kvm_vcpu_run
>> because KVM_REQ_EXIT is implied in earlier check for requests.
> 
> Actually I see more SIGUSR1 signals are intercepted by signal_pending()
> in vcpu_enter_guest() and vcpu_run() w/ win7 guest and kernel_irqchip=off.

You need more patches on the QEMU side.  I tested a version that is
mostly okay but not ready for upstream inclusion.

Paolo
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