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Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff

From: Stefan Hajnoczi
Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff
Date: Thu, 25 Jul 2013 14:41:28 +0200

On Thu, Jul 25, 2013 at 2:38 PM, Jan Kiszka <address@hidden> wrote:
> On 2013-07-25 14:35, Paolo Bonzini wrote:
>> Il 25/07/2013 14:32, Jan Kiszka ha scritto:
>>> On 2013-07-25 14:21, Alex Bligh wrote:
>>>> --On 25 July 2013 14:05:30 +0200 Stefan Hajnoczi <address@hidden>
>>>> wrote:
>>>>> Alex Bligh's series gives each AioContext its own rt_clock.  This avoids
>>>>> the need for synchronization in the simple case.  If we require timer
>>>>> access between threads then we really need to synchronize.
>>>>> You pointed out in another email that vm_clock stops when the guest is
>>>>> paused.  I think we can find a solution for I/O throttling and QED,
>>>>> which use vm_clock in the block layer.  Note that block jobs already use
>>>>> rt_clock.
>>>> I would happily at a QEMUClock of each type to AioContext. They are after
>>>> all pretty lightweight.
>>> What's the point of adding tones of QEMUClock instances? Considering
>>> proper abstraction, how are they different for each AioContext? Will
>>> they run against different clock sources, start/stop at different times?
>>> If the answer is "they have different timer list", then fix this
>>> incorrect abstraction.
>> s/QEMUClock/QEMUTimerList/ ? :)
> What do you mean? If the content of struct QEMUClock remained the same,
> that would just paper over a design mistake.

QEMUClock really isn't much more than a reference to a clock source,
an enabled/disabled flag, and a timer list.

The point of having one QEMUClock per AioContext is to allow each
thread's event loop to have its own timers, without synchronization.

What is the design mistake?  I only see poor naming.


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