linux-kernel - Re: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057: KVM: emulate lapic tsc deadline timer for guest"

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Message-ID: <CAB9v_DEz44d54tZMyFenNoNNyu3LSA6dw31S_G8MaWp7UbAULQ@mail.gmail.com>
Date:	Tue, 20 Dec 2011 10:43:00 +0200
From:	Alexey Zaytsev <alexey.zaytsev@...il.com>
To:	"Liu, Jinsong" <jinsong.liu@...el.com>
Cc:	Kernel development list <linux-kernel@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	"Garrett D'Amore" <garrett@...enta.com>
Subject: Re: [Regression, bisected] a3e06bbe8445f57eb949e6474c5a9b30f24d2057:
 KVM: emulate lapic tsc deadline timer for guest"

On Wed, Dec 14, 2011 at 11:37, Alexey Zaytsev
<alexey.zaytsev@...enta.com> wrote:
> On Mon, Dec 12, 2011 at 10:13, Liu, Jinsong <jinsong.liu@...el.com> wrote:
>> Alexey Zaytsev wrote:
>>> Hi.
>>>
>>> After a recent change, qemu --enable-kvm (both 0.15.92 and 1.0) fails
>>> to boot illumos. The OS gets stuck pretty late in the boot process,
>>> without any hints from the guest. MDB (the illumos kenrnel debugger)
>>> failed to clarify the situation at once, the kernel seems to be stuck
>>> idling. I've bisected the problem to commit
>>> a3e06bbe8445f57eb949e6474c5a9b30f24d2057. Please let me know if you
>>> need me to collect any debug information or test any patches.
>>
>> Alexey,
>>
>> Does illumos use tsc deadline timer? and do you run it at Intel platform?
>>
>> If yes, would you please help me to collect debug information by add some printk points at kvm tsc deadline timer logic? currently I totally have no clue to figure out what the issue root from :)
>> and, would you please check illumos tsc deadline timer logic by confirm whether illumos
>> 1). Enumerate tsc deadline timer capability by CPUID;
>> 2). Enable tsc deadline timer mode by lapic MMIO;
>> 3). Start tsc deadline timer by WRMSR;
>
> I think, here's what's going on. We get into
> kvm_get_lapic_tscdeadline_msr/kvm_set_lapic_tscdeadline_msr, but qemu
> does not use the KVM_CREATE_IRQCHIP ioctl, so we are running without
> vcpu->arch.apic and the functions do nothing. And the Linux guest just
> handles broken tsc a lot  better, so it survives. Both guests seem to
> work fine with qemu-kvm, which uses the ioctl.
>

Hi. Do you need any more info on thins?
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