From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-hyperv@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Sasha Levin <sashal@kernel.org>,
Stephen Hemminger <sthemmin@microsoft.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Michael Kelley <mikelley@microsoft.com>,
Stefano Stabellini <sstabellini@kernel.org>,
xen-devel@lists.xenproject.org,
Thomas Gleixner <tglx@linutronix.de>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Will Deacon <will@kernel.org>
Subject: Re: [RFC 0/6] vDSO support for Hyper-V guest on ARM64
Date: Fri, 24 Jan 2020 10:24:44 +0000 [thread overview]
Message-ID: <4cdf2188-8909-4b90-ca78-92cef520b23d@arm.com> (raw)
In-Reply-To: <20200124063215.GA93938@debian-boqun.qqnc3lrjykvubdpftowmye0fmh.lx.internal.cloudapp.net>
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Hi Boqun Feng,
On 24/01/2020 06:32, Boqun Feng wrote:
> Hi Vincenzo,
>
[...]
>>
>> I had a look to your patches and overall, I could not understand why we can't
>> use the arch_timer to do the same things you are doing with the one you
>> introduced in this series. What confuses me is that KVM works just fine with the
>> arch_timer which was designed with virtualization in mind. Why do we need
>> another one? Could you please explain?
>>
>
> Please note that the guest VM on Hyper-V for ARM64 doesn't use
> arch_timer as the clocksource. See:
>
> https://lore.kernel.org/linux-arm-kernel/1570129355-16005-7-git-send-email-mikelley@microsoft.com/
>
> , ACPI_SIG_GTDT is used for setting up Hyper-V synthetic clocksource
> and other initialization work.
>
I had a look a look at it and my question stands, why do we need another timer
on arm64?
> So just to be clear, your suggestion is
>
> 1) Hyper-V guest on ARM64 should use arch_timer as clocksource and vDSO
> will just work.
>
> or
>
> 2) Even though arch_timer is not used as the clocksource, we can still
> use it for vDSO.
>
> ?
>
Option #1 would be the preferred solution, unless there is a good reason against.
> Regards,
> Boqun
>
--
Regards,
Vincenzo
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next prev parent reply other threads:[~2020-01-24 10:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 0:19 [RFC 0/6] vDSO support for Hyper-V guest on ARM64 Boqun Feng
2019-12-16 0:19 ` [RFC 1/6] arm64: hyperv: Allow hv_get_raw_timer() definition to be overridden Boqun Feng
2019-12-16 0:19 ` [RFC 2/6] arm64: vdso: Add support for multiple vDSO data pages Boqun Feng
2019-12-16 0:19 ` [RFC 3/6] arm/arm64: clocksource: Introduce vclock_mode Boqun Feng
2019-12-16 0:19 ` [RFC 4/6] arm64: vdso: hyperv: Map tsc page into vDSO if enabled Boqun Feng
2019-12-16 0:19 ` [RFC 5/6] arm64: hyperv: Enable userspace to read cntvct Boqun Feng
2019-12-16 0:19 ` [RFC 6/6] arm64: hyperv: Enable vDSO Boqun Feng
2019-12-17 14:10 ` Vitaly Kuznetsov
2019-12-18 5:47 ` Boqun Feng
2020-01-23 10:48 ` [RFC 0/6] vDSO support for Hyper-V guest on ARM64 Vincenzo Frascino
2020-01-24 6:32 ` Boqun Feng
2020-01-24 10:24 ` Vincenzo Frascino [this message]
2020-01-28 5:58 ` Boqun Feng
2020-01-28 11:48 ` Marc Zyngier
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