From: Paolo Bonzini <pbonzini@redhat.com>
To: Marc Zyngier <marc.zyngier@arm.com>,
"Longpeng(Mike)" <longpeng2@huawei.com>,
rkrcmar@redhat.com
Cc: agraf@suse.com, borntraeger@de.ibm.com, cohuck@redhat.com,
christoffer.dall@linaro.org, james.hogan@imgtec.com,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
weidong.huang@huawei.com, arei.gonglei@huawei.com,
wangxinxin.wang@huawei.com, longpeng.mike@gmail.com
Subject: Re: [RFC] KVM: optimize the kvm_vcpu_on_spin
Date: Mon, 31 Jul 2017 16:23:55 +0200 [thread overview]
Message-ID: <a7a5e723-700a-db6f-afd4-1be8e7e9999c@redhat.com> (raw)
In-Reply-To: <85acc922-2b76-3e52-1f77-c200949b0532@arm.com>
On 31/07/2017 15:42, Marc Zyngier wrote:
>> If the vcpu(me) exit due to request a usermode spinlock, then
>> the spinlock-holder may be preempted in usermode or kernmode.
>> But if the vcpu(me) is in kernmode, then the holder must be
>> preempted in kernmode, so we should choose a vcpu in kernmode
>> as the most eligible candidate.
>
> That seems to preclude any form of locking between userspace and kernel
> (which probably wouldn't be Linux). Are you sure that this form of
> construct is not used anywhere? I have the feeling this patch could
> break this scenario...
It's just a heuristic; it would only be broken if you overcommit, and it
would be just as broken as if KVM didn't implement directed yield at all.
Paolo
prev parent reply other threads:[~2017-07-31 14:24 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-29 6:22 Longpeng(Mike)
2017-07-31 11:31 ` David Hildenbrand
2017-07-31 12:08 ` Longpeng (Mike)
2017-07-31 12:27 ` David Hildenbrand
2017-07-31 13:20 ` Paolo Bonzini
2017-08-01 3:26 ` Longpeng (Mike)
2017-08-01 8:32 ` Paolo Bonzini
2017-07-31 12:31 ` Cornelia Huck
2017-07-31 13:01 ` Longpeng (Mike)
2017-07-31 13:22 ` Christoffer Dall
2017-07-31 17:32 ` David Hildenbrand
2017-08-01 6:51 ` Cornelia Huck
2017-08-01 2:24 ` Longpeng (Mike)
2017-07-31 13:42 ` Marc Zyngier
2017-07-31 14:23 ` Paolo Bonzini [this message]
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