From: Marcelo Tosatti <mtosatti@redhat.com>
To: Glauber Costa <glommer@parallels.com>
Cc: kvm@vger.kernel.org, johnstul@us.ibm.com, jeremy@goop.org,
zamsden@gmail.com, gleb@redhat.com, avi@redhat.com,
pbonzini@redhat.com
Subject: Re: [patch 13/18] KVM: x86: pass host_tsc to read_l1_tsc
Date: Mon, 29 Oct 2012 16:45:41 -0200 [thread overview]
Message-ID: <20121029184541.GD30422@amt.cnet> (raw)
In-Reply-To: <508E9B1B.20902@parallels.com>
On Mon, Oct 29, 2012 at 07:04:59PM +0400, Glauber Costa wrote:
> On 10/24/2012 05:13 PM, Marcelo Tosatti wrote:
> > Allow the caller to pass host tsc value to kvm_x86_ops->read_l1_tsc().
> >
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Would you mind explaining why?
>
> it seems to me that rdtscll() here would be perfectly safe: the only
> case in which they wouldn't, is in a nested-vm environment running
> paravirt-linux with a paravirt tsc. In this case, it is quite likely
> that we'll want rdtscll *anyway*, instead of going to tsc directly.
Its something different (from a future patch):
"KVM added a global variable to guarantee monotonicity in the guest.
One of the reasons for that is that the time between
1. ktime_get_ts(×pec);
2. rdtscll(tsc);
Is variable. That is, given a host with stable TSC, suppose that
two VCPUs read the same time via ktime_get_ts() above.
The time required to execute 2. is not the same on those two instances
executing in different VCPUS (cache misses, interrupts...)."
Think step 1. returning the same value on both vcpus (to read the
explanation above).
next prev parent reply other threads:[~2012-10-29 18:46 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-24 13:13 [patch 00/18] pvclock vsyscall support + KVM hypervisor support (v2) Marcelo Tosatti
2012-10-24 13:13 ` [patch 01/18] KVM: x86: retain pvclock guest stopped bit in guest memory Marcelo Tosatti
2012-10-24 13:13 ` [patch 02/18] x86: pvclock: make sure rdtsc doesnt speculate out of region Marcelo Tosatti
2012-10-24 13:13 ` [patch 03/18] x86: pvclock: remove pvclock_shadow_time Marcelo Tosatti
2012-10-30 9:23 ` Avi Kivity
2012-10-30 9:24 ` Avi Kivity
2012-10-24 13:13 ` [patch 04/18] x86: pvclock: create helper for pvclock data retrieval Marcelo Tosatti
2012-10-24 13:13 ` [patch 05/18] x86: pvclock: fix flags usage race Marcelo Tosatti
2012-10-24 13:13 ` [patch 06/18] x86: pvclock: introduce helper to read flags Marcelo Tosatti
2012-10-24 13:13 ` [patch 07/18] sched: add notifier for cross-cpu migrations Marcelo Tosatti
2012-10-24 13:13 ` [patch 08/18] x86: pvclock: generic pvclock vsyscall initialization Marcelo Tosatti
2012-10-29 14:18 ` Glauber Costa
2012-10-29 14:54 ` Marcelo Tosatti
2012-10-29 17:46 ` Jeremy Fitzhardinge
2012-10-29 14:39 ` Glauber Costa
2012-10-24 13:13 ` [patch 09/18] KVM: x86: introduce facility to support vsyscall pvclock, via MSR Marcelo Tosatti
2012-10-29 14:45 ` Glauber Costa
2012-10-29 17:44 ` Jeremy Fitzhardinge
2012-10-29 18:40 ` Marcelo Tosatti
2012-10-30 7:41 ` Glauber Costa
2012-10-30 9:39 ` Avi Kivity
2012-10-31 3:12 ` Marcelo Tosatti
2012-11-02 10:21 ` Glauber Costa
2012-10-30 7:38 ` Glauber Costa
2012-10-24 13:13 ` [patch 10/18] x86: kvm guest: pvclock vsyscall support Marcelo Tosatti
2012-10-24 13:13 ` [patch 11/18] x86: vsyscall: pass mode to gettime backend Marcelo Tosatti
2012-10-29 14:47 ` Glauber Costa
2012-10-29 18:41 ` Marcelo Tosatti
2012-10-30 7:42 ` Glauber Costa
2012-10-24 13:13 ` [patch 12/18] x86: vdso: pvclock gettime support Marcelo Tosatti
2012-10-29 14:59 ` Glauber Costa
2012-10-29 18:42 ` Marcelo Tosatti
2012-10-30 7:49 ` Glauber Costa
2012-10-31 3:16 ` Marcelo Tosatti
2012-10-24 13:13 ` [patch 13/18] KVM: x86: pass host_tsc to read_l1_tsc Marcelo Tosatti
2012-10-29 15:04 ` Glauber Costa
2012-10-29 18:45 ` Marcelo Tosatti [this message]
2012-10-30 7:55 ` Glauber Costa
2012-10-24 13:13 ` [patch 14/18] time: export time information for KVM pvclock Marcelo Tosatti
2012-11-10 1:02 ` John Stultz
2012-11-13 21:07 ` Marcelo Tosatti
2012-10-24 13:13 ` [patch 15/18] KVM: x86: implement PVCLOCK_TSC_STABLE_BIT pvclock flag Marcelo Tosatti
2012-10-30 8:34 ` Glauber Costa
2012-10-31 3:19 ` [patch 15/18] KVM: x86: implement PVCLOCK_TSC_STABLE_BIT pvclock flag\ Marcelo Tosatti
2012-10-24 13:13 ` [patch 16/18] KVM: x86: notifier for clocksource changes Marcelo Tosatti
2012-10-24 13:13 ` [patch 17/18] KVM: x86: add kvm_arch_vcpu_postcreate callback, move TSC initialization Marcelo Tosatti
2012-10-24 13:13 ` [patch 18/18] KVM: x86: require matched TSC offsets for master clock Marcelo Tosatti
2012-10-31 22:46 ` [patch 00/16] pvclock vsyscall support + KVM hypervisor support (v3) Marcelo Tosatti
2012-10-31 22:46 ` [patch 01/16] KVM: x86: retain pvclock guest stopped bit in guest memory Marcelo Tosatti
2012-11-01 10:39 ` Gleb Natapov
2012-11-01 20:51 ` Marcelo Tosatti
2012-11-01 13:44 ` Glauber Costa
2012-10-31 22:46 ` [patch 02/16] x86: pvclock: make sure rdtsc doesnt speculate out of region Marcelo Tosatti
2012-11-01 11:48 ` Gleb Natapov
2012-11-01 13:49 ` Glauber Costa
2012-11-01 13:51 ` Gleb Natapov
2012-11-01 20:56 ` Marcelo Tosatti
2012-11-01 22:13 ` Gleb Natapov
2012-11-01 22:21 ` Marcelo Tosatti
2012-11-02 6:02 ` Gleb Natapov
2012-10-31 22:46 ` [patch 03/16] x86: pvclock: remove pvclock_shadow_time Marcelo Tosatti
2012-11-01 13:52 ` Glauber Costa
2012-10-31 22:47 ` [patch 04/16] x86: pvclock: create helper for pvclock data retrieval Marcelo Tosatti
2012-11-01 14:04 ` Glauber Costa
2012-11-01 20:57 ` Marcelo Tosatti
2012-10-31 22:47 ` [patch 05/16] x86: pvclock: introduce helper to read flags Marcelo Tosatti
2012-11-01 14:07 ` Glauber Costa
2012-11-01 21:08 ` Marcelo Tosatti
2012-10-31 22:47 ` [patch 06/16] sched: add notifier for cross-cpu migrations Marcelo Tosatti
2012-11-01 14:08 ` Glauber Costa
2012-10-31 22:47 ` [patch 07/16] x86: pvclock: generic pvclock vsyscall initialization Marcelo Tosatti
2012-11-01 14:19 ` Glauber Costa
2012-10-31 22:47 ` [patch 08/16] KVM: x86: introduce facility to support vsyscall pvclock, via MSR Marcelo Tosatti
2012-11-01 14:28 ` Glauber Costa
2012-11-01 21:39 ` Marcelo Tosatti
2012-11-02 10:23 ` Glauber Costa
2012-11-02 13:00 ` Marcelo Tosatti
2012-11-05 8:03 ` Glauber Costa
2012-10-31 22:47 ` [patch 09/16] x86: kvm guest: pvclock vsyscall support Marcelo Tosatti
2012-11-02 9:42 ` Glauber Costa
2012-11-05 8:35 ` Marcelo Tosatti
2012-10-31 22:47 ` [patch 10/16] x86: vdso: pvclock gettime support Marcelo Tosatti
2012-11-01 14:41 ` Glauber Costa
2012-11-01 21:42 ` Marcelo Tosatti
2012-11-02 0:33 ` Marcelo Tosatti
2012-11-02 10:25 ` Glauber Costa
2012-11-14 10:42 ` Gleb Natapov
2012-11-14 22:42 ` Marcelo Tosatti
2012-10-31 22:47 ` [patch 11/16] KVM: x86: pass host_tsc to read_l1_tsc Marcelo Tosatti
2012-10-31 22:47 ` [patch 12/16] time: export time information for KVM pvclock Marcelo Tosatti
2012-10-31 22:47 ` [patch 13/16] KVM: x86: implement PVCLOCK_TSC_STABLE_BIT pvclock flag Marcelo Tosatti
2012-10-31 22:47 ` [patch 14/16] KVM: x86: notifier for clocksource changes Marcelo Tosatti
2012-10-31 22:47 ` [patch 15/16] KVM: x86: add kvm_arch_vcpu_postcreate callback, move TSC initialization Marcelo Tosatti
2012-10-31 22:47 ` [patch 16/16] KVM: x86: require matched TSC offsets for master clock Marcelo Tosatti
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