From: Andrew Jones <drjones@redhat.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Christoffer Dall <cdall@linaro.org>,
Marc Zyngier <marc.zyngier@arm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
James Hogan <james.hogan@imgtec.com>,
Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH 6/6] KVM: perform a wake_up in kvm_make_all_cpus_request
Date: Mon, 10 Apr 2017 13:14:27 +0200 [thread overview]
Message-ID: <20170410111427.uq3neitfcssm6vbn@kamzik.brq.redhat.com> (raw)
In-Reply-To: <20170406202056.18379-7-rkrcmar@redhat.com>
On Thu, Apr 06, 2017 at 10:20:56PM +0200, Radim Krčmář 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.
Any reason we don't want kvm_vcpu_kick() to also get the
if (!(req & KVM_REQUEST_NO_WAKEUP)) optimization condition? I did some
grepping, and don't see any kicks of the requests that have been marked as
NO_WAKEUP, so nothing should change by adding it now. But the consistency
would be nice for the doc I'm writing.
Also, the condition in kvm_vcpu_kick() looks like overkill
cpu != me && (unsigned)cpu < nr_cpu_ids && cpu_online(cpu)
How could vcpu->cpu ever be any offline/invalid cpu, other than -1? The
condition in kvm_make_all_cpus_request() makes more sense to me
cpu != -1 && cpu != me
I guess a lot this stuff is planned for a larger requests rework, when
kicks get integrated with requests? I'm a bit anxious, though, as it
changes how I document stuff now, and even how I approach the ARM series.
For example, if kvm_make_request() already integrated kvm_vcpu_kick(),
which means also adding the smp_mb__after_atomic(), like
kvm_make_all_cpus_request() has, then I wouldn't need to add the smp_mb()
to kvm_arch_vcpu_should_kick().
Thanks,
drew
>
> 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
> 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.
>
> 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 a486c6ad27a6..1db503bab3dc 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_arch_vcpu_should_kick(vcpu))
> cpumask_set_cpu(cpu, cpus);
> --
> 2.12.0
>
next prev parent reply other threads:[~2017-04-10 11:14 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-06 20:20 [PATCH 0/6] KVM: towards maintainable kvm_make_all_cpus_request() Radim Krčmář
2017-04-06 20:20 ` [PATCH RFC 1/6] KVM: fix guest_mode optimization in kvm_make_all_cpus_request() Radim Krčmář
2017-04-06 21:02 ` James Hogan
2017-04-10 15:59 ` Andrew Jones
2017-04-11 10:43 ` James Hogan
2017-04-11 5:25 ` Paolo Bonzini
2017-04-11 9:37 ` James Hogan
2017-04-11 19:31 ` Radim Krčmář
2017-04-11 19:45 ` Paolo Bonzini
2017-04-11 20:45 ` Radim Krčmář
2017-04-12 0:15 ` Paolo Bonzini
2017-04-07 10:47 ` Christian Borntraeger
2017-04-06 20:20 ` [PATCH 2/6] KVM: use kvm_{test,clear}_request instead of {test,clear}_bit Radim Krčmář
2017-04-07 10:55 ` Christian Borntraeger
2017-04-07 12:24 ` Radim Krčmář
2017-04-07 14:05 ` Radim Krčmář
2017-04-06 20:20 ` [PATCH 3/6] KVM: x86: use kvm_make_request instead of set_bit Radim Krčmář
2017-04-07 8:18 ` David Hildenbrand
2017-04-06 20:20 ` [PATCH 4/6] KVM: remove #ifndef CONFIG_S390 around kvm_vcpu_wake_up Radim Krčmář
2017-04-07 11:01 ` Christian Borntraeger
2017-04-06 20:20 ` [PATCH RFC 5/6] KVM: mark requests that do not need a wakeup Radim Krčmář
2017-04-07 8:27 ` Marc Zyngier
2017-04-07 12:29 ` Radim Krčmář
2017-04-06 20:20 ` [PATCH 6/6] KVM: perform a wake_up in kvm_make_all_cpus_request Radim Krčmář
2017-04-10 11:14 ` Andrew Jones [this message]
2017-04-11 5:34 ` Paolo Bonzini
2017-04-11 12:04 ` Andrew Jones
2017-04-11 5:37 ` Paolo Bonzini
2017-04-11 8:55 ` Paolo Bonzini
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20170410111427.uq3neitfcssm6vbn@kamzik.brq.redhat.com \
--to=drjones@redhat.com \
--cc=borntraeger@de.ibm.com \
--cc=cdall@linaro.org \
--cc=cornelia.huck@de.ibm.com \
--cc=james.hogan@imgtec.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=marc.zyngier@arm.com \
--cc=paulus@ozlabs.org \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).