From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Avi Kivity <avi@redhat.com>
Cc: Glauber Costa <glommer@redhat.com>,
Dan Magenheimer <dan.magenheimer@oracle.com>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
kurt.hackel@oracle.com, the arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Glauber de Oliveira Costa <gcosta@redhat.com>,
Xen-devel <xen-devel@lists.xensource.com>,
Keir Fraser <keir.fraser@eu.citrix.com>,
zach.brown@oracle.com, chris.mason@oracle.com,
Ingo Molnar <mingo@redhat.com>
Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation
Date: Wed, 28 Oct 2009 10:47:37 -0700 [thread overview]
Message-ID: <4AE883B9.4050409@goop.org> (raw)
In-Reply-To: <4AE81011.4040904@redhat.com>
On 10/28/09 02:34, Avi Kivity wrote:
> On 10/28/2009 11:29 AM, Glauber Costa wrote:
>>> How can you reliably measure performance in a virtualized environment?
>>>
>> If we loop gettimeofday(), I would expect the vsyscall-based version
>> not to show
>> up in strace, right?
>>
>
> Much better to have an API for this. Life is hacky enough already.
My point is that if an app cares about property X then it should just
measure property X. The fact that gettimeofday is a vsyscall is just an
implementation detail that apps don't really care about. What they care
about is whether gettimeofday is fast or not.
If the environment has such unstable timing that the effect can't be
measured, then it is moot whether its a vsyscall or not (but in that
case its almost certainly better to use the standard API rather than
trying to roll your own timesource with rdtsc).
J
next prev parent reply other threads:[~2009-10-28 17:47 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-06 0:50 [PATCH RFC] Extending pvclock down to usermode for vsyscall Jeremy Fitzhardinge
2009-10-06 0:50 ` [PATCH 1/5] x86/pvclock: make sure rdtsc doesn't speculate out of region Jeremy Fitzhardinge
2009-10-06 0:50 ` [PATCH 2/5] x86/pvclock: no need to use strong read barriers in pvclock_get_time_values Jeremy Fitzhardinge
2009-10-06 0:50 ` [PATCH 3/5] x86/pvclock: add vsyscall implementation Jeremy Fitzhardinge
2009-10-06 9:04 ` Avi Kivity
2009-10-06 14:19 ` Dan Magenheimer
2009-10-06 15:11 ` Avi Kivity
2009-10-06 18:46 ` [Xen-devel] " Jeremy Fitzhardinge
2009-10-07 10:25 ` Avi Kivity
2009-10-07 19:29 ` Jeremy Fitzhardinge
2009-10-07 20:09 ` Avi Kivity
2009-10-07 21:19 ` Jeremy Fitzhardinge
2009-10-07 21:37 ` Avi Kivity
2009-10-07 21:51 ` Jeremy Fitzhardinge
2009-10-07 21:53 ` Avi Kivity
2009-10-07 20:48 ` Dan Magenheimer
2009-10-07 21:08 ` Avi Kivity
2009-10-07 22:36 ` Dan Magenheimer
2009-10-10 0:24 ` Jeremy Fitzhardinge
2009-10-10 18:10 ` Avi Kivity
2009-10-12 18:20 ` Jeremy Fitzhardinge
2009-10-12 18:29 ` Avi Kivity
2009-10-12 19:13 ` Jeremy Fitzhardinge
2009-10-13 6:39 ` Avi Kivity
2009-10-13 20:00 ` Jeremy Fitzhardinge
2009-10-14 12:32 ` Avi Kivity
2009-10-15 19:17 ` Jeremy Fitzhardinge
2009-10-27 17:29 ` Dan Magenheimer
2009-10-27 18:20 ` Jeremy Fitzhardinge
2009-10-28 5:52 ` Avi Kivity
2009-10-28 9:29 ` Glauber Costa
2009-10-28 9:34 ` Avi Kivity
2009-10-28 17:47 ` Jeremy Fitzhardinge [this message]
2009-10-29 12:13 ` Avi Kivity
2009-10-29 13:03 ` Chris Mason
2009-10-29 14:46 ` Dan Magenheimer
2009-10-29 15:07 ` Avi Kivity
2009-10-29 15:55 ` Dan Magenheimer
2009-10-29 16:15 ` Dan Magenheimer
2009-11-01 9:28 ` Avi Kivity
2009-11-02 15:28 ` Dan Magenheimer
2009-11-02 15:41 ` Avi Kivity
2009-11-01 9:32 ` Avi Kivity
2009-11-02 15:46 ` Dan Magenheimer
2009-11-03 5:12 ` Avi Kivity
2009-11-04 20:30 ` Dan Magenheimer
2009-11-05 6:47 ` Avi Kivity
2009-11-05 14:52 ` Dan Magenheimer
2009-11-05 15:07 ` Keir Fraser
2009-11-04 21:19 ` john stultz
2009-11-04 21:28 ` Dan Magenheimer
2009-11-05 0:02 ` john stultz
2009-11-05 0:45 ` Dan Magenheimer
2009-10-06 0:50 ` [PATCH 4/5] x86/fixmap: add a predicate for usermode fixmaps Jeremy Fitzhardinge
2009-10-06 10:23 ` [Xen-devel] " Jan Beulich
2009-10-06 18:47 ` Jeremy Fitzhardinge
2009-10-06 0:50 ` [PATCH 5/5] xen/time: add pvclock_clocksource_vread support Jeremy Fitzhardinge
2009-10-06 10:28 ` [Xen-devel] " Jan Beulich
2009-10-06 18:48 ` Jeremy Fitzhardinge
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