From: "Nadav Har'El" <nyh@math.technion.ac.il>
To: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Cc: Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
LKML <linux-kernel@vger.kernel.org>, KVM <kvm@vger.kernel.org>
Subject: Re: [PATCH v3 2/3] KVM: send IPI to vcpu only when it's in guest mode
Date: Wed, 12 Jan 2011 11:54:28 +0200 [thread overview]
Message-ID: <20110112095428.GA15835@fermat.math.technion.ac.il> (raw)
In-Reply-To: <4D2D5AEF.1070006@cn.fujitsu.com>
On Wed, Jan 12, 2011, Xiao Guangrong wrote about "[PATCH v3 2/3] KVM: send IPI to vcpu only when it's in guest mode":
> We can interrupt the vcpu only when it's running in guest mode
> to reduce IPI
Hi,
I am afraid there's a risk of confusion between the new
vcpu->mode = IN_GUEST_MODE;
and the existing
is_guest_mode() (i.e., vcpu->arch.hflags & HF_GUEST_MASK)
The latter says that the virtual cpu is in guest mode (i.e., the guest used
VMLAUNCH and is runnning a nested guest), while the former says that the
physical CPU that this vcpu is currently being run on, is in guest mode - or
in other words, this vcpu is currently running.
I'm not sure what is the best way to resolve this potential for confusion.
Maybe on of them is better renamed (e.g., instead of vcpu->mode = IN_GUEST_MODE
have something like vcpu->running = NOW_RUNNING). Or maybe some good comments
need to to be written to explain the situation.
Actually, I just noticed that there's already a vcpu->guest_mode which you
are apparently replacing, so the potential for confusion is already in the
current code... I.e., in the current code, is_guest_mode(vcpu) does NOT check
vcpu->guest_mode...
--
Nadav Har'El | Wednesday, Jan 12 2011, 7 Shevat 5771
nyh@math.technion.ac.il |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Hi! I'm a signature virus! Copy me into
http://nadav.harel.org.il |your signature to help me spread!
next prev parent reply other threads:[~2011-01-12 9:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-12 7:39 [PATCH v3 1/3] KVM: fix rcu usage warning in kvm_arch_vcpu_ioctl_set_sregs() Xiao Guangrong
2011-01-12 7:40 ` [PATCH v3 2/3] KVM: send IPI to vcpu only when it's in guest mode Xiao Guangrong
2011-01-12 9:54 ` Nadav Har'El [this message]
2011-01-12 9:59 ` Avi Kivity
2011-01-12 7:41 ` [PATCH v3 3/3] KVM: make make_all_cpus_request() lockless Xiao Guangrong
2011-01-19 5:16 ` [PATCH v3 1/3] KVM: fix rcu usage warning in kvm_arch_vcpu_ioctl_set_sregs() Xiao Guangrong
2011-01-19 18:13 ` Marcelo Tosatti
2011-01-20 3:03 ` Xiao Guangrong
2011-01-20 15:27 ` Marcelo Tosatti
2011-01-27 2:35 ` Xiao Guangrong
2011-01-27 13:15 ` Avi Kivity
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