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Date: Fri, 26 Jul 2013 11:19:19 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff
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To: Alex Bligh <alex@alex.org.uk>
Cc: Kevin Wolf <kwolf@redhat.com>, Anthony Liguori <anthony@codemonkey.ws>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, Liu Ping Fan <qemulist@gmail.com>, Stefan Hajnoczi <stefanha@redhat.com>, Jan Kiszka <jan.kiszka@siemens.com>

Il 26/07/2013 11:08, Alex Bligh ha scritto:
> 
> 
> --On 26 July 2013 10:43:45 +0200 Stefan Hajnoczi <stefanha@gmail.com>
> wrote:
> 
>> block.c and block/qed.c use vm_clock because block drivers should not do
>> guest I/O while the vm is stopped.  This is especially true during live
>> migration where it's important to hand off the image file from the
>> source host to the destination host with good cache consistency.  The
>> source host is not allowed to modify the image file anymore once the
>> destination host has resumed the guest.
>>
>> Block jobs use rt_clock because they aren't considered guest I/O.
> 
> That's going to be 'interesting' if qemu-img uses a block driver that
> uses a timer, as I don't think the vm timer is running when qemu-img
> is running.

Yes, it is, see stubs/cpu-get-clock.c:

#include "qemu-common.h"
#include "qemu/timer.h"

int64_t cpu_get_clock(void)
{
    return get_clock_realtime();
}


vm_clock becomes a synonym of rt_clock basically.

Paolo