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From: Jan Kiszka <jan.kiszka@web.de>
To: Michael Tokarev <mjt@tls.msk.ru>
Cc: Avi Kivity <avi@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Gerd Hoffmann <kraxel@redhat.com>, KVM list <kvm@vger.kernel.org>,
	Gleb Natapov <gleb@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	qemu-stable <qemu-stable@nongnu.org>
Subject: Re: [PATCH uq/master] kvm: i8254: Finish time conversion fix
Date: Tue, 14 Aug 2012 09:41:24 +0200	[thread overview]
Message-ID: <502A0124.1020005@web.de> (raw)
In-Reply-To: <50294A1F.9070104@msgid.tls.msk.ru>

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On 2012-08-13 20:40, Michael Tokarev wrote:
> On 13.08.2012 22:18, Jan Kiszka wrote:
>> 0cdd3d1444 fixed reading back the counter load time from the kernel
>> while assuming the kernel would always update its load time on writing
>> the state. That is only true for channel 1, and so pit_get_channel_info
>> returned wrong output pin states for high counter values.
>>
>> Fix this by applying the offset also on kvm_pit_put. For this purpose,
>> we cache the clock offset in KVMPITState, only updating it on VM state
>> changes or when we write the state while the VM is stopped.
> 
> Wug.  The fix (consisting of two halves) appears to be quite messy.

I will split it up into offset caching and application to kvm_pit_put.

> Is it a (temporary) workaround or a real solution?

No, this is the real solution. It may look complex, but it is required
due to the different time bases of the in-kernel PIT and QEMU's vmclock.
We didn't care about this in qemu-kvm in the past, but upstream now
actually supports migration between in-kernel and user space models, and
it also supports the PC speaker with the in-kernel PIT enabled.

> 
> And yes, this second half fixes the reported issue with grub timekeeping,
> and should fix the seabios problem as well (so it shouldn't be necessary
> to mess with timekeeping in seabios anymore).

Thanks, great to hear!

Jan



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WARNING: multiple messages have this Message-ID (diff)
From: Jan Kiszka <jan.kiszka@web.de>
To: Michael Tokarev <mjt@tls.msk.ru>
Cc: KVM list <kvm@vger.kernel.org>, Gleb Natapov <gleb@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	qemu-stable <qemu-stable@nongnu.org>, Avi Kivity <avi@redhat.com>,
	Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: [Qemu-devel] [PATCH uq/master] kvm: i8254: Finish time conversion fix
Date: Tue, 14 Aug 2012 09:41:24 +0200	[thread overview]
Message-ID: <502A0124.1020005@web.de> (raw)
In-Reply-To: <50294A1F.9070104@msgid.tls.msk.ru>

[-- Attachment #1: Type: text/plain, Size: 1396 bytes --]

On 2012-08-13 20:40, Michael Tokarev wrote:
> On 13.08.2012 22:18, Jan Kiszka wrote:
>> 0cdd3d1444 fixed reading back the counter load time from the kernel
>> while assuming the kernel would always update its load time on writing
>> the state. That is only true for channel 1, and so pit_get_channel_info
>> returned wrong output pin states for high counter values.
>>
>> Fix this by applying the offset also on kvm_pit_put. For this purpose,
>> we cache the clock offset in KVMPITState, only updating it on VM state
>> changes or when we write the state while the VM is stopped.
> 
> Wug.  The fix (consisting of two halves) appears to be quite messy.

I will split it up into offset caching and application to kvm_pit_put.

> Is it a (temporary) workaround or a real solution?

No, this is the real solution. It may look complex, but it is required
due to the different time bases of the in-kernel PIT and QEMU's vmclock.
We didn't care about this in qemu-kvm in the past, but upstream now
actually supports migration between in-kernel and user space models, and
it also supports the PC speaker with the in-kernel PIT enabled.

> 
> And yes, this second half fixes the reported issue with grub timekeeping,
> and should fix the seabios problem as well (so it shouldn't be necessary
> to mess with timekeeping in seabios anymore).

Thanks, great to hear!

Jan



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  reply	other threads:[~2012-08-14  7:41 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-09 18:27 TSC in qem[-kvm] 1.1+ and in-kernel irqchip Michael Tokarev
2012-08-09 18:27 ` [Qemu-devel] " Michael Tokarev
2012-08-09 19:06 ` Marcelo Tosatti
2012-08-09 19:06   ` [Qemu-devel] " Marcelo Tosatti
     [not found]   ` <20120809204748.GA32346@amt.cnet>
2012-08-09 21:36     ` Michael Tokarev
2012-08-09 21:36       ` [Qemu-devel] " Michael Tokarev
2012-08-10  7:33 ` Gleb Natapov
2012-08-10  7:33   ` Gleb Natapov
2012-08-10  9:24   ` Michael Tokarev
2012-08-10  9:24     ` Michael Tokarev
2012-08-12  8:10     ` Gleb Natapov
2012-08-12  8:10       ` [Qemu-devel] " Gleb Natapov
2012-08-12  9:24       ` Michael Tokarev
2012-08-12  9:24         ` [Qemu-devel] " Michael Tokarev
2012-08-13 13:07         ` Jan Kiszka
2012-08-13 13:07           ` [Qemu-devel] " Jan Kiszka
2012-08-13 13:16           ` Michael Tokarev
2012-08-13 13:16             ` Michael Tokarev
2012-08-13 13:41             ` Jan Kiszka
2012-08-13 13:41               ` Jan Kiszka
2012-08-13 18:18             ` [PATCH uq/master] kvm: i8254: Finish time conversion fix Jan Kiszka
2012-08-13 18:18               ` [Qemu-devel] " Jan Kiszka
2012-08-13 18:40               ` Michael Tokarev
2012-08-13 18:40                 ` [Qemu-devel] " Michael Tokarev
2012-08-14  7:41                 ` Jan Kiszka [this message]
2012-08-14  7:41                   ` Jan Kiszka

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