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Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb |
Date: |
Mon, 29 Jul 2013 13:21:40 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
Il 29/07/2013 10:10, liu ping fan ha scritto:
> On Mon, Jul 29, 2013 at 2:30 PM, Paolo Bonzini <address@hidden> wrote:
>> Il 29/07/2013 05:16, Liu Ping Fan ha scritto:
>>> After disabling the QemuClock, we should make sure that no QemuTimers
>>> are still in flight. To implement that, the caller of disabling will
>>> wait until the last user's exit.
>>>
>>> Note, the callers of qemu_clock_enable() should be sync by themselves,
>>> not protected by this patch.
>>>
>>> Signed-off-by: Liu Ping Fan <address@hidden>
>>
>> This is an interesting approach.
>>
>>> - if (!clock->enabled)
>>> - return;
>>> + atomic_inc(&clock->using);
>>> + if (unlikely(!clock->enabled)) {
>>> + goto exit;
>>> + }
>>
>> This can return directly, it doesn't need to increment and decrement
>> clock->using.
>>
> Here is a race condition like the following
Ah, I see.
Still this seems a bit backwards. Most of the time you will have no one
on the wait_using condvar, but you are almost always signaling the
condvar (should be broadcast BTW)...
Paolo
- [Qemu-devel] [RFC v2 0/5] arm AioContext with its own timer stuff, Liu Ping Fan, 2013/07/28
- [Qemu-devel] [RFC v2 1/5] timer: protect timers_state with lock, Liu Ping Fan, 2013/07/28
- [Qemu-devel] [RFC v2 2/5] timer: pick out timer list info from QemuClock, Liu Ping Fan, 2013/07/28
- [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, Liu Ping Fan, 2013/07/28
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, Paolo Bonzini, 2013/07/29
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, liu ping fan, 2013/07/29
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb,
Paolo Bonzini <=
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, liu ping fan, 2013/07/29
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, Paolo Bonzini, 2013/07/30
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, Alex Bligh, 2013/07/30
- Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync between disable and timer's cb, Paolo Bonzini, 2013/07/30
[Qemu-devel] [RFC v2 4/5] timer: associate three timerlists with AioContext, Liu Ping Fan, 2013/07/28
[Qemu-devel] [RFC v2 5/5] timer: run timers on aio_poll, Liu Ping Fan, 2013/07/28