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From: Marcelo Tosatti <mtosatti@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Maxim Levitsky <mlevitsk@redhat.com>,
	kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Oliver Upton <oupton@google.com>, Ingo Molnar <mingo@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	open list <linux-kernel@vger.kernel.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Wanpeng Li <wanpengli@tencent.com>,
	Borislav Petkov <bp@alien8.de>, Jim Mattson <jmattson@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Joerg Roedel <joro@8bytes.org>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH 0/2] RFC: Precise TSC migration
Date: Tue, 1 Dec 2020 12:02:05 -0300	[thread overview]
Message-ID: <20201201150205.GA42117@fuller.cnet> (raw)
In-Reply-To: <877dq1hc2s.fsf@nanos.tec.linutronix.de>

On Tue, Dec 01, 2020 at 02:48:11PM +0100, Thomas Gleixner wrote:
> On Mon, Nov 30 2020 at 16:16, Marcelo Tosatti wrote:
> >> Besides, Linux guests don't sync the TSC via IA32_TSC write,
> >> but rather use IA32_TSC_ADJUST which currently doesn't participate
> >> in the tsc sync heruistics.
> >
> > Linux should not try to sync the TSC with IA32_TSC_ADJUST. It expects
> > the BIOS to boot with synced TSCs.
> 
> That's wishful thinking.
> 
> Reality is that BIOS tinkerers fail to get it right. TSC_ADJUST allows
> us to undo the wreckage they create.
> 
> Thanks,
> 
>         tglx

Have not seen any multicore Dell/HP systems require that.

Anyway, for QEMU/KVM it should be synced (unless there is a bug
in the sync logic in the first place).


  reply	other threads:[~2020-12-01 19:29 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-30 13:35 [PATCH 0/2] RFC: Precise TSC migration Maxim Levitsky
2020-11-30 13:35 ` [PATCH 1/2] KVM: x86: implement KVM_SET_TSC_PRECISE/KVM_GET_TSC_PRECISE Maxim Levitsky
2020-11-30 14:33   ` Paolo Bonzini
2020-11-30 15:58     ` Maxim Levitsky
2020-11-30 17:01       ` Paolo Bonzini
2020-12-01 19:43   ` Thomas Gleixner
2020-12-03 11:11     ` Maxim Levitsky
2020-11-30 13:35 ` [PATCH 2/2] KVM: x86: introduce KVM_X86_QUIRK_TSC_HOST_ACCESS Maxim Levitsky
2020-11-30 13:54   ` Paolo Bonzini
2020-11-30 14:11     ` Maxim Levitsky
2020-11-30 14:15       ` Paolo Bonzini
2020-11-30 15:33         ` Maxim Levitsky
2020-11-30 13:38 ` [PATCH 0/2] RFC: Precise TSC migration (summary) Maxim Levitsky
2020-11-30 16:54 ` [PATCH 0/2] RFC: Precise TSC migration Andy Lutomirski
2020-11-30 16:59   ` Paolo Bonzini
2020-11-30 19:16 ` Marcelo Tosatti
2020-12-01 12:30   ` Maxim Levitsky
2020-12-01 19:48     ` Marcelo Tosatti
2020-12-03 11:39       ` Maxim Levitsky
2020-12-03 20:18         ` Marcelo Tosatti
2020-12-07 13:00           ` Maxim Levitsky
2020-12-01 13:48   ` Thomas Gleixner
2020-12-01 15:02     ` Marcelo Tosatti [this message]
2020-12-03 11:51       ` Maxim Levitsky
2020-12-01 14:01   ` Thomas Gleixner
2020-12-01 16:19     ` Andy Lutomirski
2020-12-03 11:57       ` Maxim Levitsky
2020-12-01 19:35 ` Thomas Gleixner
2020-12-03 11:41   ` Paolo Bonzini
2020-12-03 12:47   ` Maxim Levitsky
2020-11-30 13:38 Maxim Levitsky
2020-11-30 13:38 ` Maxim Levitsky

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