linux-kernel - Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU is blocked

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Date:	Fri, 5 Jun 2015 18:59:15 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Wu, Feng" <feng.wu@...el.com>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"gleb@...nel.org" <gleb@...nel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"dwmw2@...radead.org" <dwmw2@...radead.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>,
	"eric.auger@...aro.org" <eric.auger@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU is
 blocked

On Tue, Apr 14, 2015 at 07:37:44AM +0000, Wu, Feng wrote:
> 
> 
> > -----Original Message-----
> > From: Marcelo Tosatti [mailto:mtosatti@...hat.com]
> > Sent: Tuesday, March 31, 2015 7:56 AM
> > To: Wu, Feng
> > Cc: hpa@...or.com; tglx@...utronix.de; mingo@...hat.com; x86@...nel.org;
> > gleb@...nel.org; pbonzini@...hat.com; dwmw2@...radead.org;
> > joro@...tes.org; alex.williamson@...hat.com; jiang.liu@...ux.intel.com;
> > eric.auger@...aro.org; linux-kernel@...r.kernel.org;
> > iommu@...ts.linux-foundation.org; kvm@...r.kernel.org
> > Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when vCPU
> > is blocked
> > 
> > On Mon, Mar 30, 2015 at 04:46:55AM +0000, Wu, Feng wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Marcelo Tosatti [mailto:mtosatti@...hat.com]
> > > > Sent: Saturday, March 28, 2015 3:30 AM
> > > > To: Wu, Feng
> > > > Cc: hpa@...or.com; tglx@...utronix.de; mingo@...hat.com;
> > x86@...nel.org;
> > > > gleb@...nel.org; pbonzini@...hat.com; dwmw2@...radead.org;
> > > > joro@...tes.org; alex.williamson@...hat.com; jiang.liu@...ux.intel.com;
> > > > eric.auger@...aro.org; linux-kernel@...r.kernel.org;
> > > > iommu@...ts.linux-foundation.org; kvm@...r.kernel.org
> > > > Subject: Re: [v3 24/26] KVM: Update Posted-Interrupts Descriptor when
> > vCPU
> > > > is blocked
> > > >
> > > > On Fri, Mar 27, 2015 at 06:34:14AM +0000, Wu, Feng wrote:
> > > > > > > Currently, the following code is executed before local_irq_disable() is
> > > > called,
> > > > > > > so do you mean 1)moving local_irq_disable() to the place before it. 2)
> > after
> > > > > > interrupt
> > > > > > > is disabled, set KVM_REQ_EVENT in case the ON bit is set?
> > > > > >
> > > > > > 2) after interrupt is disabled, set KVM_REQ_EVENT in case the ON bit
> > > > > > is set.
> > > > >
> > > > > Here is my understanding about your comments here:
> > > > > - Disable interrupts
> > > > > - Check 'ON'
> > > > > - Set KVM_REQ_EVENT if 'ON' is set
> > > > >
> > > > > Then we can put the above code inside " if
> > > > (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) "
> > > > > just like it used to be. However, I still have some questions about this
> > > > comment:
> > > > >
> > > > > 1. Where should I set KVM_REQ_EVENT? In function vcpu_enter_guest(),
> > or
> > > > other places?
> > > >
> > > > See below:
> > > >
> > > > > If in vcpu_enter_guest(), since currently local_irq_disable() is called after
> > > > 'KVM_REQ_EVENT'
> > > > > is checked, is it helpful to set KVM_REQ_EVENT after local_irq_disable() is
> > > > called?
> > > >
> > > >         local_irq_disable();
> > > >
> > > > 	*** add code here ***
> > >
> > > So we need add code like the following here, right?
> > >
> > >           if ('ON' is set)
> > >               kvm_make_request(KVM_REQ_EVENT, vcpu);
> > 
> 
> Hi Marcelo,
> 
> I changed the code as above, then I found that the ping latency was extremely big, (70ms - 400ms).
> I digged into it and got the root cause. We cannot use "checking-on" as the judgment, since 'ON'
> can be cleared by hypervisor software in lots of places. In this case, KVM_REQ_EVENT cannot be
> set when we check 'ON' bit, hence the interrupts are not injected to the guest in time.
> 
> Please refer to the following code, in which 'ON' bit can be cleared:
> 
> apic_find_highest_irr () --> vmx_sync_pir_to_irr () --> pi_test_and_clear_on()
> 
> Searching from the code step by step, apic_find_highest_irr() can be called by many other guys.
> 
> Thanks,

Ok then, ignore my suggestion.

Can you resend the latest version please ?


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