From: David Hildenbrand <dahi@linux.vnet.ibm.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: kvm@vger.kernel.org, pbonzini@redhat.com, gleb@kernel.org,
jfrei@linux.vnet.ibm.com, cornelia.huck@de.ibm.com
Subject: Re: [PATCH RFC 1/2] KVM: don't check for PF_VCPU when yielding
Date: Wed, 26 Nov 2014 10:23:19 +0100 [thread overview]
Message-ID: <20141126102319.2f92c64b@thinkpad-w530> (raw)
In-Reply-To: <54758692.5000906@de.ibm.com>
> This change is a trade-off.
> PRO: This patch would improve the case of preemption on s390. This is probably a corner case as most distros have preemption off anyway.
> CON: The downside is that kvm_vcpu_yield_to is called also from kvm_vcpu_on_spin. Here we want to avoid the scheduler overhead for a wrong decision.
Won't most of that part be covered by:
if (!ACCESS_ONCE(vcpu->preempted))
vcpu->preempted is only set when scheduled out involuntarily. It is cleared
when scheduled in. s390 sets it manually, to speed up waking up a vcpu.
So when our task is scheduled in (an PF_VCPU is set), this check will already
avoid scheduler overhead in kvm_vcpu_on_spin() or am I missing something?
next prev parent reply other threads:[~2014-11-26 9:23 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-25 16:04 [PATCH RFC 0/2] assign each vcpu an owning thread and improve yielding David Hildenbrand
2014-11-25 16:04 ` [PATCH RFC 1/2] KVM: don't check for PF_VCPU when yielding David Hildenbrand
2014-11-26 7:51 ` Christian Borntraeger
2014-11-26 9:23 ` David Hildenbrand [this message]
2014-11-26 9:31 ` Christian Borntraeger
2014-11-28 10:08 ` Raghavendra KT
2014-11-28 10:58 ` Christian Borntraeger
2014-11-28 11:40 ` Raghavendra K T
2014-12-01 9:54 ` David Hildenbrand
2014-12-03 12:53 ` Paolo Bonzini
2014-12-03 13:02 ` Paolo Bonzini
2014-12-03 13:04 ` David Hildenbrand
2014-11-25 16:04 ` [PATCH RFC 2/2] KVM: thread creating a vcpu is the owner of that vcpu David Hildenbrand
2014-11-26 7:54 ` Christian Borntraeger
2014-12-03 12:53 ` Paolo Bonzini
2014-12-03 12:12 ` [PATCH RFC 0/2] assign each vcpu an owning thread and improve yielding David Hildenbrand
2014-12-03 12:54 ` Paolo Bonzini
2014-12-03 13:00 ` David Hildenbrand
2014-12-03 13:00 ` Christian Borntraeger
2014-12-03 13:06 ` Paolo Bonzini
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