From: David Matlack <dmatlack@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm list" <kvm@vger.kernel.org>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Andy Lutomirski" <luto@kernel.org>,
"Peter Hornyack" <peterhornyack@google.com>,
"X86 ML" <x86@kernel.org>
Subject: Re: [PATCH 2/2] x86, kvm: use kvmclock to compute TSC deadline value
Date: Fri, 9 Sep 2016 13:05:41 -0700 [thread overview]
Message-ID: <CALzav=eR1eVv4kd7hyQ1J6TDNar4XniRY-V+cWLYb9qwBv6FAA@mail.gmail.com> (raw)
In-Reply-To: <42be43c0-bb0c-8b01-9e36-39ced43209c0@redhat.com>
On Fri, Sep 9, 2016 at 9:38 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 09/09/2016 00:13, David Matlack wrote:
>> Hi Paolo,
>>
>> On Tue, Sep 6, 2016 at 3:29 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> Bad things happen if a guest using the TSC deadline timer is migrated.
>>> The guest doesn't re-calibrate the TSC after migration, and the
>>> TSC frequency can and will change unless your processor supports TSC
>>> scaling (on Intel this is only Skylake) or your data center is perfectly
>>> homogeneous.
>>
>> Sorry, I forgot to follow up on our discussion in v1. One thing we
>> discussed there was using the APIC Timer to workaround a changing TSC
>> rate. You pointed out KVM's TSC deadline timer got a nice performance
>> boost recently, which makes it preferable. Does it makes sense to
>> apply the same optimization (using the VMX preemption timer) to the
>> APIC Timer, instead of creating a new dependency on kvmclock?
>
> Hi, yes it does. If we go that way kvmclock.c should be patched to
> blacklist the TSC deadline timer. However, I won't have time to work on
> it anytime soon, so _if I get reviews_ I'll take this patch first.
Got it, thanks for the context.
next prev parent reply other threads:[~2016-09-09 20:06 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-06 22:29 [PATCH v2 0/2] if running under KVM, use kvmclock to compute TSC deadline value Paolo Bonzini
2016-09-06 22:29 ` [PATCH 1/2] x86: paravirt: add local_apic_timer_interrupt to pv_ops Paolo Bonzini
2016-09-07 6:25 ` kbuild test robot
2016-09-07 6:33 ` kbuild test robot
2016-09-06 22:29 ` [PATCH 2/2] x86, kvm: use kvmclock to compute TSC deadline value Paolo Bonzini
2016-09-08 22:13 ` David Matlack
2016-09-09 16:38 ` Paolo Bonzini
2016-09-09 20:05 ` David Matlack [this message]
2016-10-11 4:05 ` Wanpeng Li
2016-09-15 15:09 ` Radim Krčmář
2016-09-15 16:00 ` Paolo Bonzini
2016-09-15 19:59 ` Radim Krčmář
2016-09-15 21:02 ` Paolo Bonzini
2016-09-16 14:59 ` Radim Krčmář
2016-09-16 15:06 ` Paolo Bonzini
2016-09-16 15:24 ` Radim Krčmář
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