From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Dan Magenheimer <dan.magenheimer@oracle.com>
Cc: Xen-devel <xen-devel@lists.xensource.com>,
kurt.hackel@oracle.com, arch/x86 maintainers <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Glauber de Oliveira Costa <gcosta@redhat.com>,
Avi Kivity <avi@redhat.com>,
chris.mason@oracle.com
Subject: Re: [Xen-devel] [PATCH 05/12] xen/pvclock: add monotonicity check
Date: Thu, 15 Oct 2009 12:19:22 -0700 [thread overview]
Message-ID: <4AD775BA.30704@goop.org> (raw)
In-Reply-To: <c7f37ead-3cf2-4277-a44e-425a7b940d31@default>
On 10/15/09 06:27, Dan Magenheimer wrote:
> I understand but you are now essentially emulating a
> reliable platform timer with a potentially unreliable
> (but still high resolution) per-CPU timer AND probably
> delivering that result to userland.
>
> Read_tsc should only be used if either CONSTANT_TSC
> or TSC_RELIABLE is true, so read_tsc is guaranteed
> to be monotonically-strictly-increasing by hardware
> (and enforced for CONSTANT_TSC by check_tsc_warp
> at boot).
>
read_tsc clearly isn't expected to produce absolutely globally monotonic
results; if it were then the check wouldn't be necessary.
J
next prev parent reply other threads:[~2009-10-15 19:20 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-14 19:28 [GIT PULL RFC] pvclock cleanups and pvclock vsyscall support Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 01/12] x86/vsyscall: use common implementation for vgetcpu Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 02/12] x86/vgetcpu: ignore tcache in common code Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 03/12] x86/vsyscall: use common implementation for vgettimeofday Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 04/12] kvm/pvclock: add monotonicity check Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 05/12] xen/pvclock: " Jeremy Fitzhardinge
2009-10-15 3:26 ` [Xen-devel] " Dan Magenheimer
2009-10-15 5:24 ` Jeremy Fitzhardinge
2009-10-15 13:27 ` Dan Magenheimer
2009-10-15 19:19 ` Jeremy Fitzhardinge [this message]
2009-10-16 1:32 ` john stultz
2009-10-16 3:10 ` Jeremy Fitzhardinge
2009-10-16 17:58 ` john stultz
2009-10-18 8:18 ` Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 06/12] x86/pvclock: make sure rdtsc doesn't speculate out of region Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 07/12] pvclock: there's no need to copy time_info into shadow Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 08/12] x86: create specific X86_VSYSCALL config variable Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 09/12] sched: add notifier for cross-cpu migrations Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 10/12] x86/pvclock: add vsyscall implementation Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 11/12] x86/fixmap: add a predicate for usermode fixmaps Jeremy Fitzhardinge
2009-10-14 19:28 ` [PATCH 12/12] xen/time: add pvclock_clocksource_vread support Jeremy Fitzhardinge
2009-10-15 6:51 ` [GIT PULL RFC] pvclock cleanups and pvclock vsyscall support Avi Kivity
2009-10-15 19:46 ` Jeremy Fitzhardinge
2009-10-18 6:43 ` Avi Kivity
2009-10-18 8:18 ` Jeremy Fitzhardinge
2009-10-18 8:23 ` Avi Kivity
2009-10-18 8:44 ` Jeremy Fitzhardinge
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