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 04:37:11 +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



> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Yang Zhang
> Sent: Monday, December 21, 2015 10:06 AM
> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> rkrcmar@...hat.com
> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v2 1/2] KVM: x86: Use vector-hashing to deliver lowest-
> priority interrupts
> 
> On 2015/12/21 9:50, Wu, Feng wrote:
> >
> >
> >> -----Original Message-----
> >> From: Yang Zhang [mailto:yang.zhang.wz@...il.com]
> >> Sent: Monday, December 21, 2015 9:46 AM
> >> To: Wu, Feng <feng.wu@...el.com>; pbonzini@...hat.com;
> >> rkrcmar@...hat.com
> >> Cc: kvm@...r.kernel.org; linux-kernel@...r.kernel.org
> >> 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?

Thanks,
Feng
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