linux-kernel - Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os statistics from host side

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Message-Id: <1902473858.2078.481.camel@ymzhang.sh.intel.com>
Date:	Mon, 15 Apr 2030 16:57:38 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, zhiteng.huang@...el.com,
	tim.c.chen@...el.com, Arnaldo Carvalho de Melo <acme@...radead.org>
Subject: Re: [PATCH V3] perf & kvm: Enhance perf to collect KVM guest os
 statistics from host side

On Thu, 2010-04-15 at 11:05 +0300, Avi Kivity wrote:
> On 04/15/2030 04:04 AM, Zhang, Yanmin wrote:
> >
> >> An even more accurate way to determine this is to check whether the
> >> interrupt frame points back at the 'int $2' instruction.  However we
> >> plan to switch to a self-IPI method to inject the NMI, and I'm not sure
> >> wether APIC NMIs are accepted on an instruction boundary or whether
> >> there's some latency involved.
> >>      
> > Yes. But the frame pointer checking seems a little complicated.
> >    
> 
> An even bigger disadvantage is that it won't work with Sheng's patch, 
> self-NMIs are not synchronous.
> 
> >>>    	trace_kvm_entry(vcpu->vcpu_id);
> >>> +
> >>> +	percpu_write(current_vcpu, vcpu);
> >>>    	kvm_x86_ops->run(vcpu);
> >>> +	percpu_write(current_vcpu, NULL);
> >>>
> >>>        
> >> If you move this around the 'int $2' instructions you will close the
> >> race, as a stray NMI won't catch us updating the rip cache.  But that
> >> depends on whether self-IPI is accepted on the next instruction or not.
> >>      
> > Right. The kernel part has dependency on the self-IPI implementation.
> > I will move above percpu_write(current_vcpu, vcpu) (or a new wrapper function)
> > just around 'int $2'.
> >
> >    
> 
> Or create a new function to inject the interrupt in x86.c.  That will 
> reduce duplication between svm.c and vmx.c.
I checked svm.c and it seems svm.c doesn't trigger a NMI to host if the NMI
happens in guest os. In addition, svm_complete_interrupts is called after
interrupt is enabled.


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