linux-kernel - Re: [PATCH v6] kvm: make vcpu life cycle separated from kvm instance

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Message-ID: <CAFgQCTtFFOYY09Edg_ibNTRYfxHh1HRjqgpRyBy7jUZYJgEJxA@mail.gmail.com>
Date:	Thu, 29 Dec 2011 22:03:03 +0800
From:	Liu ping fan <kernelfans@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com, gleb@...hat.com, mtosatti@...hat.com,
	xiaoguangrong.eric@...il.com, jan.kiszka@....de,
	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
Subject: Re: [PATCH v6] kvm: make vcpu life cycle separated from kvm instance

On Wed, Dec 28, 2011 at 5:53 PM, Avi Kivity <avi@...hat.com> wrote:
> On 12/28/2011 08:54 AM, Liu ping fan wrote:
>> >>
>> >>   struct kvm_vcpu {
>> >>       struct kvm *kvm;
>> >> +     struct list_head list;
>> >>   #ifdef CONFIG_PREEMPT_NOTIFIERS
>> >>       struct preempt_notifier preempt_notifier;
>> >>   #endif
>> >> @@ -251,12 +252,14 @@ struct kvm {
>> >>       struct mm_struct *mm; /* userspace tied to this vm */
>> >>       struct kvm_memslots *memslots;
>> >>       struct srcu_struct srcu;
>> >> +     struct srcu_struct srcu_vcpus;
>> >> +
>> >
>> > Another srcu.  This alone is worth explaining in the changelog IMO.
>> >
>> Sorry, but why? I think it is just a srcu, and because it has
>> different aim and want a independent grace period, so not multiplex
>> kvm->srcu.
>
> There is Documentation/virtual/kvm/locking.txt for that.
>
> btw, why does it have to be srcu?  Is rcu insufficient?
>
Just to survive from "if (yield_to(task, 1)) in  kvm_vcpu_on_spin()",

> Why do we want an independent grace period, is hotunplugging a vcpu that
> much different from hotunplugging memory?
>
I thought that if less readers on the same srcu lock, then
synchronize_srcu_expedited() may success to return more quickly.

Thanks and regards,
ping fan
> --
> error compiling committee.c: too many arguments to function
>
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