From: Andrew Cooper <andrew.cooper3@citrix.com>
To: "jaeyong.yoo@samsung.com" <jaeyong.yoo@samsung.com>
Cc: "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>
Subject: Re: A simple question regarding hvm_context_save
Date: Fri, 31 May 2013 11:55:19 +0100 [thread overview]
Message-ID: <51A88197.1040706@citrix.com> (raw)
In-Reply-To: <32587091.297611369997199444.JavaMail.weblogic@epv6ml06>
On 31/05/13 11:46, Jaeyong Yoo wrote:
> Hello,
> I'm reading live migration related code and got a simple question
> in function hvm_context_save:
>
> static int hvm_save_cpu_ctxt(struct domain *d, hvm_domain_context_t *h)
> {
> blah...
> /* We don't need to save state for a vcpu that is down; the restore
> * code will leave it down if there is nothing saved. */
> if ( test_bit(_VPF_down, &v->pause_flags) )
> continue;
> blah...
>
> In the above, if the vcpu is paused, we don't need to store cpu registers
> (since vcpu structure already stored them). But, as far as I know, before
> we save the hvm context, we suspend the domain, which calls shutdown
> sched_op, and the vcpu is paused.
_VPF_down is only one possible pause reason. See
xen/include/xen/sched.h for all of them.
In particular, _VPF_migrating is a different pause reason.
If a VCPU is down, the guest is required to reinitialise it from
scratch. This is why the state does not need saving.
~Andrew
> Then, I guess testing pause_flags always returns down and we don't
> need to store cpu ctxts. Do I miss something here?
>
> best,
> Jaeyong
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
prev parent reply other threads:[~2013-05-31 10:55 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-31 10:46 A simple question regarding hvm_context_save Jaeyong Yoo
2013-05-31 10:53 ` Ian Campbell
2013-05-31 10:55 ` Andrew Cooper [this message]
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