From: Peter Zijlstra <peterz@infradead.org>
To: Glauber Costa <glommer@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
aliguori@us.ibm.com, Rik van Riel <riel@redhat.com>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
Avi Kivity <avi@redhat.com>, tglx <tglx@linutronix.de>
Subject: Re: [PATCH v2 2/6] KVM-HV: KVM Steal time implementation
Date: Mon, 31 Jan 2011 12:07:11 +0100 [thread overview]
Message-ID: <1296472031.15234.367.camel@laptop> (raw)
In-Reply-To: <1296244340-15173-3-git-send-email-glommer@redhat.com>
On Fri, 2011-01-28 at 14:52 -0500, Glauber Costa wrote:
> + u64 to = (get_kernel_ns() - vcpu->arch.this_time_out);
> + /*
> + * using nanoseconds introduces noise, which accumulates easily
> + * leading to big steal time values. We want, however, to keep the
> + * interface nanosecond-based for future-proofness.
> + */
> + to /= NSEC_PER_USEC;
> + to *= NSEC_PER_USEC;
This just doesn't make any sense at all, you use the most expensive and
accurate kernel interface to get ns resolution timestamps (ktime_get),
and then you truncate the stuff to usec for some totally weird and
unexplained reason.
If ktime_get is wrong all our time-keeping is out the window.
next prev parent reply other threads:[~2011-01-31 11:06 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-28 19:52 [PATCH v2 0/6] KVM Steal time, new submission Glauber Costa
2011-01-28 19:52 ` [PATCH v2 1/6] KVM-HDR: KVM Steal time implementation Glauber Costa
2011-01-29 1:28 ` Rik van Riel
2011-01-28 19:52 ` [PATCH v2 2/6] KVM-HV: " Glauber Costa
2011-01-29 1:46 ` Rik van Riel
2011-01-30 13:13 ` Avi Kivity
2011-02-01 15:48 ` Glauber Costa
2011-02-01 17:09 ` Avi Kivity
2011-02-01 19:58 ` Glauber Costa
2011-02-02 10:09 ` Avi Kivity
2011-01-31 11:07 ` Peter Zijlstra [this message]
2011-01-28 19:52 ` [PATCH v2 3/6] KVM-GST: KVM Steal time accounting Glauber Costa
2011-01-29 1:16 ` Jeremy Fitzhardinge
2011-01-29 1:27 ` Glauber Costa
2011-01-29 1:53 ` Rik van Riel
2011-01-30 14:04 ` Avi Kivity
2011-01-30 16:45 ` lidong chen
2011-02-01 15:58 ` Glauber Costa
2011-02-01 15:57 ` Glauber Costa
2011-02-02 10:11 ` Avi Kivity
2011-02-02 10:51 ` Avi Kivity
2011-02-02 11:57 ` Glauber Costa
2011-01-28 19:52 ` [PATCH v2 4/6] KVM-GST: KVM Steal time registration Glauber Costa
2011-01-29 2:16 ` Rik van Riel
2011-01-30 13:16 ` Avi Kivity
2011-02-01 15:53 ` Glauber Costa
2011-02-01 16:17 ` Peter Zijlstra
2011-02-01 17:00 ` Glauber Costa
2011-02-01 17:44 ` Peter Zijlstra
2011-02-01 20:20 ` Venkatesh Pallipadi
2011-01-31 11:11 ` Peter Zijlstra
2011-01-28 19:52 ` [PATCH v2 5/6] KVM-GST: adjust scheduler cpu power Glauber Costa
2011-01-31 11:25 ` Peter Zijlstra
2011-01-31 11:27 ` Peter Zijlstra
2011-02-01 15:59 ` Glauber Costa
2011-02-01 16:19 ` Peter Zijlstra
2011-02-01 16:22 ` Glauber Costa
2011-02-01 18:59 ` Peter Zijlstra
2011-02-01 19:55 ` Glauber Costa
2011-02-01 20:04 ` Peter Zijlstra
2011-01-28 19:52 ` [PATCH v2 6/6] Describe KVM_MSR_STEAL_TIME Glauber Costa
2011-01-30 13:19 ` Avi Kivity
2011-02-01 15:54 ` Glauber Costa
2011-02-02 10:14 ` Avi Kivity
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