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From: "Dong, Eddie" <eddie.dong@intel.com>
To: "Avi Kivity" <avi@qumranet.com>
Cc: "Glauber de Oliveira Costa" <gcosta@redhat.com>,
	<linux-kernel@vger.kernel.org>, <jeremy@goop.org>,
	<hollisb@us.ibm.com>, <kvm-devel@lists.sourceforge.net>
Subject: RE: [kvm-devel] [PATCH 2/3] kvmclock - the host part.
Date: Wed, 14 Nov 2007 08:41:16 +0800	[thread overview]
Message-ID: <10EA09EFD8728347A513008B6B0DA77A025DFCCF@pdsmsx411.ccr.corp.intel.com> (raw)
In-Reply-To: <4739CD03.90406@qumranet.com>

>> 
>> +	kvm_get_msr(vcpu, MSR_IA32_TIME_STAMP_COUNTER,
>> +			  &vcpu->hv_clock.last_tsc);
>> +
>> +	ktime_get_ts(&ts);
>> +	vcpu->hv_clock.now_ns = ts.tv_nsec + (NSEC_PER_SEC *
>> (u64)ts.tv_sec); +	vcpu->hv_clock.wc_sec = get_seconds();
>> 
>> I am even thinking we have to disable interrupt between these lines,
>> otherwise guest wall clock may see backward time source when
>> calculating the delta TSC since last vcpu->hv_clock.now_ns update.
>> 
> 
> That's true.  While we do need to handle vcpu migration and
> descheduling, the code sequence you note needs to be as atomic as
> possible. 
> 

Yes VCPU migration is another issue. Since the physical platform TSC is 
totally different across migration, so we can't expose host TSC to
guest.
For KVM, it should be simple to just use guest_TSC (=HOST_TSC + offset).

thanks, eddie

  reply	other threads:[~2007-11-14  0:42 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-11-08 22:39 [PATCH 0/3] Kvm clocksource, new spin Glauber de Oliveira Costa
2007-11-08 22:39 ` [PATCH 1/3] include files for kvmclock Glauber de Oliveira Costa
2007-11-08 22:39   ` [PATCH 2/3] kvmclock - the host part Glauber de Oliveira Costa
2007-11-08 22:39     ` [PATCH 3/3] kvmclock implementation, the guest part Glauber de Oliveira Costa
2007-11-11 10:17     ` [PATCH 2/3] kvmclock - the host part Avi Kivity
2007-11-13 11:28       ` Glauber de Oliveira Costa
2007-11-13 14:44         ` Avi Kivity
2007-11-13  5:00     ` [kvm-devel] " Dong, Eddie
2007-11-13 11:54       ` Glauber de Oliveira Costa
2007-11-13 12:08         ` Izik Eidus
2007-11-13 14:47         ` Avi Kivity
2007-11-13 15:23           ` Dong, Eddie
2007-11-13 16:12             ` Avi Kivity
2007-11-14  0:41               ` Dong, Eddie [this message]
2007-11-09  8:37   ` [PATCH 1/3] include files for kvmclock Gerd Hoffmann
2007-11-11  9:15     ` Avi Kivity

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