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RE: [Xen-devel] [PATCH] replace rdtsc emulation-vs-native xen boot optio
| To: | Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
|---|---|
| Subject: | RE: [Xen-devel] [PATCH] replace rdtsc emulation-vs-native xen boot option with per-domain (hypervisor part) |
| From: | Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> |
| Date: | Mon, 28 Sep 2009 16:36:03 -0700 (PDT) |
| Cc: | "Xen-Devel \(E-mail\)" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> |
| Delivery-date: | Mon, 28 Sep 2009 16:36:48 -0700 |
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> On 09/28/09 15:43, Dan Magenheimer wrote:
> > PV ones too. An app doesn't have any idea (and doesn't
> > and shouldn't care) if it is running on a PV or HVM domain.
>
> Well, it shouldn't be enabled by default. That slows down all rdtsc
> operations for the benefit of very niche applications. The Xen
> clocksource assumes that rdtsc is fast, unemulated and in need of
> correction.
>
> If someone really needs an artificial tsc, then they can enable the
> option for themselves.
While I understand and sympathize (and the idealistic side of me even
agrees with) your position, let me argue your point "they can enable
the option for themselves" by mangling a famous movie quote:
"In a cloud, no-one can hear rdtsc scream"
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