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Date: Fri, 17 Feb 2017 18:55:02 +0100 (CET) From: Thomas Gleixner <tglx@...utronix.de> To: Andy Lutomirski <luto@...capital.net> cc: Vitaly Kuznetsov <vkuznets@...hat.com>, "K. Y. Srinivasan" <kys@...rosoft.com>, X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Stephen Hemminger <sthemmin@...rosoft.com>, Dexuan Cui <decui@...rosoft.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, devel@...uxdriverproject.org, Linux Virtualization <virtualization@...ts.linux-foundation.org> Subject: Re: [PATCH v2 0/3] x86/vdso: Add Hyper-V TSC page clocksource support On Fri, 17 Feb 2017, Andy Lutomirski wrote: > On Fri, Feb 17, 2017 at 2:14 AM, Vitaly Kuznetsov <vkuznets@...hat.com> wrote: > > Not only. As far as I understand (and I *think* K. Y. pointed this out) > > when VM is migrating to another host TSC page clocksource is disabled for > > extended period of time so we're better off reading from MSR than > > looping here. With regards to VDSO this means reverting to doing normal > > syscall. > > That's a crappy design. The guest really ought to be able to > distinguish "busy, try again" from "bail and use MSR". > > Thomas, I can see valid reasons why the hypervisor might want to > temporarily disable shared page-based timing, but I think it's silly > that it's conflated with indicating "retry". It's beyond silly if that's the case. > But if this is indeed the ABI, we're stuck with it. No argument.
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