From: Marcelo Tosatti <mtosatti@redhat.com>
To: Peter Lieven <pl@dlhnet.de>
Cc: Vadim Rozenfeld <vrozenfe@redhat.com>,
kvm@vger.kernel.org, pbonzini@redhat.com
Subject: Re: [RFC PATCH v3 1/2] add support for Hyper-V reference time counter
Date: Thu, 2 Jan 2014 18:05:55 -0200 [thread overview]
Message-ID: <20140102200555.GA9687@amt.cnet> (raw)
In-Reply-To: <52C58EE7.1040004@dlhnet.de>
On Thu, Jan 02, 2014 at 05:08:07PM +0100, Peter Lieven wrote:
> > Not using irq disable/enable pairs. The subtraction is not dependant on
> > any particular time.
> >
> > local_irq_disable();
> > now_ns = get_kernel_ns();
> > local_irq_enable();
> > delta = user_ns.clock - now_ns;
> >
> > Any interrupt that would affect the value of get_kernel_ns(), would
> > have a similar effect before the interrupts are disabled. So the
> > disable/enable pair achieves nothing in practice. It was copied from
> > kvm_guest_time_update.
> >
> >
>
> Thanks for clarifying. What about get_kernel_ns() can't this be interrupted?
>
> Peter
It can handle interrupts.
Disabling interrupts there is used when a
{rdtsc, system_time=get_kernel_ns()} tuple is wanted, to reduce
the physical time difference between execution of rdtsc and get_kernel_ns().
next prev parent reply other threads:[~2014-01-02 20:06 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-12-08 11:33 [RFC PATCH v3 0/2] Hyper-V timers Vadim Rozenfeld
2013-12-08 11:33 ` [RFC PATCH v3 1/2] add support for Hyper-V reference time counter Vadim Rozenfeld
2013-12-09 14:23 ` Paolo Bonzini
2013-12-10 10:46 ` Vadim Rozenfeld
2013-12-11 18:53 ` Marcelo Tosatti
2013-12-11 18:59 ` Marcelo Tosatti
2013-12-12 9:33 ` Paolo Bonzini
2014-01-02 16:52 ` Peter Lieven
2014-01-07 9:36 ` Vadim Rozenfeld
2014-01-07 17:52 ` Peter Lieven
2014-01-08 9:40 ` Vadim Rozenfeld
2014-01-08 10:15 ` Peter Lieven
2014-01-08 10:44 ` Vadim Rozenfeld
2014-01-08 11:48 ` Peter Lieven
2014-01-08 12:12 ` Vadim Rozenfeld
2014-01-08 14:54 ` Peter Lieven
2014-01-08 20:08 ` Vadim Rozenfeld
2014-01-08 22:20 ` Peter Lieven
2014-01-09 11:10 ` Vadim Rozenfeld
2014-01-12 12:08 ` Vadim Rozenfeld
2014-01-12 20:35 ` Peter Lieven
2014-01-02 13:15 ` Peter Lieven
2014-01-02 13:57 ` Marcelo Tosatti
2014-01-02 16:08 ` Peter Lieven
2014-01-02 20:05 ` Marcelo Tosatti [this message]
2014-01-13 12:10 ` Vadim Rozenfeld
2013-12-08 11:33 ` [RFC PATCH v3 2/2] add support for Hyper-V partition reference time enlightenment Vadim Rozenfeld
2013-12-09 14:32 ` Paolo Bonzini
2013-12-10 11:23 ` Vadim Rozenfeld
2013-12-10 16:52 ` Paolo Bonzini
2013-12-11 10:58 ` Vadim Rozenfeld
2013-12-11 12:28 ` Paolo Bonzini
2013-12-11 19:28 ` Marcelo Tosatti
2013-12-11 19:27 ` Marcelo Tosatti
2013-12-12 9:34 ` Paolo Bonzini
2014-01-14 4:11 ` Vadim Rozenfeld
2014-01-14 13:54 ` Marcelo Tosatti
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