From: Paolo Bonzini <pbonzini@redhat.com>
To: "Cornelia Huck" <cornelia.huck@de.ibm.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Christoffer Dall <cdall@linaro.org>,
Andrew Jones <drjones@redhat.com>,
Marc Zyngier <marc.zyngier@arm.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
James Hogan <james.hogan@imgtec.com>,
Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH v2 5/9] KVM: perform a wake_up in kvm_make_all_cpus_request
Date: Thu, 27 Apr 2017 14:15:57 +0200 [thread overview]
Message-ID: <246ae7e1-f381-6672-3573-278620a48547@redhat.com> (raw)
In-Reply-To: <20170427140655.40eebb34.cornelia.huck@de.ibm.com>
On 27/04/2017 14:06, Cornelia Huck wrote:
> On Wed, 26 Apr 2017 22:32:23 +0200
> Radim Krčmář <rkrcmar@redhat.com> wrote:
>
>> We want to have kvm_make_all_cpus_request() to be an optmized version of
>>
>> kvm_for_each_vcpu(i, vcpu, kvm) {
>> kvm_make_request(vcpu, request);
>> kvm_vcpu_kick(vcpu);
>> }
>>
>> and kvm_vcpu_kick() wakes up the target vcpu. We know which requests do
>> not need the wake up and use it to optimize the loop.
>>
>> Thanks to that, this patch doesn't change the behavior of current users
>> (the all don't need the wake up) and only prepares for future where the
>
> s/the all/they all/
>
>> wake up is going to be needed.
>>
>> I think that most requests do not need the wake up, so we would flip the
>> bit then.
>>
>> kvm_vcpu_kick() will get this condition after it is merged with
>> kvm_make_request() because we currently don't know which request is being
>> kicked.
>
> I find this sentence confusing: not all kicks are directly related to
> requests.
I agree, it is backwards. Changing to "Later on, kvm_make_request()
will take care of kicking too, using this bit to make the decision
whether to kick or not".
Paolo
>>
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>> virt/kvm/kvm_main.c | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index e5d52b46b531..3772f7dcc72d 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -186,6 +186,9 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req)
>> /* Set ->requests bit before we read ->mode. */
>> smp_mb__after_atomic();
>>
>> + if (!(req & KVM_REQUEST_NO_WAKEUP))
>> + kvm_vcpu_wake_up(vcpu);
>> +
>> if (cpus != NULL && cpu != -1 && cpu != me &&
>> kvm_vcpu_exiting_guest_mode(vcpu) != OUTSIDE_GUEST_MODE)
>> cpumask_set_cpu(cpu, cpus);
>
> The code change looks good to me.
>
next prev parent reply other threads:[~2017-04-27 12:16 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-26 20:32 [PATCH v2 0/9] KVM: towards maintainable kvm_make_all_cpus_request() Radim Krčmář
2017-04-26 20:32 ` [PATCH v2 1/9] KVM: add kvm_{test,clear}_request to replace {test,clear}_bit Radim Krčmář
2017-04-27 11:33 ` Andrew Jones
2017-04-27 11:38 ` Cornelia Huck
2017-04-26 20:32 ` [PATCH v2 2/9] KVM: x86: always use kvm_make_request instead of set_bit Radim Krčmář
2017-04-27 11:33 ` Andrew Jones
2017-04-26 20:32 ` [PATCH v2 3/9] KVM: remove #ifndef CONFIG_S390 around kvm_vcpu_wake_up Radim Krčmář
2017-04-27 11:45 ` Cornelia Huck
2017-05-03 16:05 ` Radim Krčmář
2017-05-03 16:16 ` [PATCH v3] " Radim Krčmář
2017-05-03 17:04 ` Cornelia Huck
2017-04-26 20:32 ` [PATCH v2 4/9] KVM: mark requests that do not need a wakeup Radim Krčmář
2017-04-27 11:35 ` Andrew Jones
2017-04-27 12:00 ` Cornelia Huck
2017-04-26 20:32 ` [PATCH v2 5/9] KVM: perform a wake_up in kvm_make_all_cpus_request Radim Krčmář
2017-04-27 11:36 ` Andrew Jones
2017-04-27 12:06 ` Cornelia Huck
2017-04-27 12:15 ` Paolo Bonzini [this message]
2017-04-26 20:32 ` [PATCH v2 6/9] KVM: add explicit barrier to kvm_vcpu_kick Radim Krčmář
2017-04-26 20:32 ` [PATCH v2 7/9] KVM: improve arch vcpu request defining Radim Krčmář
2017-04-27 12:11 ` Cornelia Huck
2017-04-26 20:32 ` [PATCH v2 8/9] KVM: return if kvm_vcpu_wake_up() did wake up the VCPU Radim Krčmář
2017-04-27 11:41 ` Andrew Jones
2017-04-26 20:32 ` [PATCH v2 9/9] KVM: mark requests that need synchronization Radim Krčmář
2017-04-27 11:55 ` Andrew Jones
2017-04-27 12:36 ` Paolo Bonzini
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