linux-kernel - RE: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-priority interrupts

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Date:	Tue, 22 Dec 2015 07:19:08 +0000
From:	"Wu, Feng" <feng.wu@...el.com>
To:	Yang Zhang <yang.zhang.wz@...il.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"rkrcmar@...hat.com" <rkrcmar@...hat.com>
CC:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Jiang Liu (jiang.liu@...ux.intel.com)" <jiang.liu@...ux.intel.com>,
	"Wu, Feng" <feng.wu@...el.com>
Subject: RE: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver
 lowest-priority interrupts

Hi Radim/Paolo,

> -----Original Message-----
> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
> Sent: Tuesday, December 22, 2015 3:14 PM
> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> rkrcmar@...hat.com
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Jiang Liu
> (jiang.liu@...ux.intel.com) <jiang.liu@...ux.intel.com>
> Subject: Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-
> priority interrupts
> 
> On 2015/12/22 14:59, Wu, Feng wrote:
> >
> >
> >> -----Original Message-----
> >> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
> >> Sent: Tuesday, December 22, 2015 2:49 PM
> >> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> >> rkrcmar@...hat.com
> >> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org; Jiang Liu
> >> (jiang.liu@...ux.intel.com) <jiang.liu@...ux.intel.com>
> >> Subject: Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-
> >> priority interrupts
> >>
> >>>>>>
> >>>>>> On 2015/12/16 9:37, Feng Wu wrote:
> >>>>>>> Use vector-hashing to deliver lowest-priority interrupts, As an
> >>>>>>> example, modern Intel CPUs in server platform use this method to
> >>>>>>> handle lowest-priority interrupts.
> >>>>>>>
> >>>>>>> Signed-off-by: Feng Wu <feng.wu@...el.com>
> >>>>>>> ---
> >>>>>>>      arch/x86/kvm/irq_comm.c | 27 ++++++++++++++++++-----
> >>>>>>>      arch/x86/kvm/lapic.c    | 57
> >>>>>> ++++++++++++++++++++++++++++++++++++++++---------
> >>>>>>>      arch/x86/kvm/lapic.h    |  2 ++
> >>>>>>>      arch/x86/kvm/x86.c      |  9 ++++++++
> >>>>>>>      arch/x86/kvm/x86.h      |  1 +
> >>>>>>>      5 files changed, 81 insertions(+), 15 deletions(-)
> >>>>>>>
> >>>>>>>      bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct
> kvm_lapic
> >>>> *src,
> >>>>>>>      		struct kvm_lapic_irq *irq, int *r, unsigned long
> >> *dest_map)
> >>>>>>>      {
> >>>>>>> @@ -731,17 +747,38 @@ bool kvm_irq_delivery_to_apic_fast(struct
> kvm
> >>>>>> *kvm, struct kvm_lapic *src,
> >>>>>>>      		dst = map->logical_map[cid];
> >>>>>>>
> >>>>>>>      		if (kvm_lowest_prio_delivery(irq)) {
> >>>>>>> -			int l = -1;
> >>>>>>> -			for_each_set_bit(i, &bitmap, 16) {
> >>>>>>> -				if (!dst[i])
> >>>>>>> -					continue;
> >>>>>>> -				if (l < 0)
> >>>>>>> -					l = i;
> >>>>>>> -				else if (kvm_apic_compare_prio(dst[i]-
> >vcpu,
> >>>>>> dst[l]->vcpu) < 0)
> >>>>>>> -					l = i;
> >>>>>>> +			if (!kvm_vector_hashing_enabled()) {
> >>>>>>> +				int l = -1;
> >>>>>>> +				for_each_set_bit(i, &bitmap, 16) {
> >>>>>>> +					if (!dst[i])
> >>>>>>> +						continue;
> >>>>>>> +					if (l < 0)
> >>>>>>> +						l = i;
> >>>>>>> +					else if
> (kvm_apic_compare_prio(dst[i]-
> >>>>>>> vcpu, dst[l]->vcpu) < 0)
> >>>>>>> +						l = i;
> >>>>>>> +				}
> >>>>>>> +				bitmap = (l >= 0) ? 1 << l : 0;
> >>>>>>> +			} else {
> >>>>>>> +				int idx = 0;
> >>>>>>> +				unsigned int dest_vcpus = 0;
> >>>>>>> +
> >>>>>>> +				for_each_set_bit(i, &bitmap, 16) {
> >>>>>>> +					if (!dst[i]
> >>>>>> && !kvm_lapic_enabled(dst[i]->vcpu)) {
> >>>>>>
> >>>>>> It should be or(||) not and (&&).
> >>>>>
> >>>>> Oh, you are right! My negligence! Thanks for pointing this out, Yang!
> >>>>
> >>>> btw, i think the kvm_lapic_enabled check is wrong here? Why need it here?
> >>>
> >>> If the lapic is not enabled, I think we cannot recognize it as a candidate, can
> >> we?
> >>> Maybe Radim can confirm this, Radim, what is your option?
> >>
> >> Lapic can be disable by hw or sw. Here we only need to check the hw is
> >> enough which is already covered while injecting the interrupt into
> >> guest. I remember we(Glab, Macelo and me) have discussed it several ago,
> >> but i cannot find the mail thread.
> >
> > But if the lapic is disabled by software, we cannot still inject interrupts to
> > it, can we?
> 
> Yes, We cannot inject the normal interrupt. But this already covered by
> current logic and add a check here seems meaningless. Conversely, it may
> do bad thing..
> 

Let's wait for Radim/Paolo's opinions about this.

Thanks,
Feng
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