From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, Wei Liu <wei.liu2@citrix.com>,
Jan Beulich <jbeulich@suse.com>,
Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH RFC] x86/lapic: remove the PIT usage to calibrate the lapic timer
Date: Wed, 19 Sep 2018 18:47:54 +0200 [thread overview]
Message-ID: <87o9ctxwlh.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20180919162554.80569-1-roger.pau@citrix.com> (Roger Pau Monne's message of "Wed, 19 Sep 2018 18:25:54 +0200")
Roger Pau Monne <roger.pau@citrix.com> writes:
> And instead use NOW which is based on the TSC. This was already used
> when running in shim mode, since there's likely no PIT in that
> environment.
>
> Remove printing the CPU frequency, since it's already printed earlier
> at boot, and getting the CPU frequency against the TSC without any
> external reference timer is pointless.
>
> The motivation behind this change is to allow Xen to boot on HyperV
> gen2 instances, which lack a PIT.
When on Hyper-V, LAPIC frequency can easily be queried from
HV_X64_MSR_APIC_FREQUENCY (and that's what Linux does nowdays). This, of
course, only if Hyper-V provides the interface but it always does.
--
Vitaly
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next prev parent reply other threads:[~2018-09-19 16:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-19 16:25 [PATCH RFC] x86/lapic: remove the PIT usage to calibrate the lapic timer Roger Pau Monne
2018-09-19 16:47 ` Vitaly Kuznetsov [this message]
2018-09-19 16:48 ` Wei Liu
2018-09-20 8:18 ` Jan Beulich
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