From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: lantianyu1986@gmail.com
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>,
linux-arch@vger.kernel.org, linux-hyperv@vger.kernel.org,
linux-kernel@vger.kernel.org, luto@kernel.org,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
hpa@zytor.com, x86@kernel.org, kys@microsoft.com,
haiyangz@microsoft.com, sthemmin@microsoft.com,
sashal@kernel.org, daniel.lezcano@linaro.org, arnd@arndb.de,
michael.h.kelley@microsoft.com, ashal@kernel.org
Subject: Re: [PATCH 0/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function
Date: Mon, 29 Jul 2019 12:59:26 +0200 [thread overview]
Message-ID: <87zhkxksxd.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20190729075243.22745-1-Tianyu.Lan@microsoft.com>
lantianyu1986@gmail.com writes:
> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>
> Hyper-V guests use the default native_sched_clock() in pv_ops.time.sched_clock
> on x86. But native_sched_clock() directly uses the raw TSC value, which
> can be discontinuous in a Hyper-V VM. Add the generic hv_setup_sched_clock()
> to set the sched clock function appropriately. On x86, this sets
> pv_ops.time.sched_clock to read the Hyper-V reference TSC value that is
> scaled and adjusted to be continuous.
Hypervisor can, in theory, disable TSC page and then we're forced to use
MSR-based clocksource but using it as sched_clock() can be very slow,
I'm afraid.
On the other hand, what we have now is probably worse: TSC can,
actually, jump backwards (e.g. on migration) and we're breaking the
requirements for sched_clock().
--
Vitaly
next prev parent reply other threads:[~2019-07-29 10:59 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 7:52 [PATCH 0/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function lantianyu1986
2019-07-29 7:52 ` [PATCH 1/2] clocksource/Hyper-v: Allocate Hyper-V tsc page statically lantianyu1986
2019-08-12 18:39 ` Michael Kelley
2019-07-29 7:52 ` [PATCH 2/2] clocksource/Hyper-V: Add Hyper-V specific sched clock function lantianyu1986
2019-08-12 18:41 ` Michael Kelley
2019-07-29 10:59 ` Vitaly Kuznetsov [this message]
2019-07-29 11:09 ` [PATCH 0/2] " Peter Zijlstra
2019-07-29 12:13 ` Vitaly Kuznetsov
2019-07-30 13:41 ` Tianyu Lan
2019-08-12 19:22 ` Michael Kelley
2019-08-13 8:33 ` Vitaly Kuznetsov
2019-08-20 14:32 ` Michael Kelley
2019-08-21 7:15 ` Vitaly Kuznetsov
2019-08-21 8:54 ` Vitaly Kuznetsov
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