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Date: Wed, 28 Apr 2010 22:04:16 +0530
From: Amit Shah <amit.shah@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH v6 18/18] virtio-serial-bus: wake up
	iothread upon guest read notification
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Marcelo Tosatti <mtosatti@redhat.com>, qemu list <qemu-devel@nongnu.org>, Juan Quintela <quintela@redhat.com>

On (Wed) Apr 28 2010 [08:25:59], Anthony Liguori wrote:
> On 04/28/2010 02:29 AM, Amit Shah wrote:
>> On (Tue) Apr 27 2010 [12:41:27], Anthony Liguori wrote:
>>    
>>> On 04/27/2010 07:34 AM, Amit Shah wrote:
>>>      
>>>> From: Marcelo Tosatti<mtosatti@redhat.com>
>>>>
>>>> Wake up iothread when buffers are consumed.
>>>>
>>>> Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
>>>> Signed-off-by: Amit Shah<amit.shah@redhat.com>
>>>>
>>>>        
>>> What's the race here?  This looks very odd to me.
>>>      
>> When the guest indicates it has added buffers to the vq, the iothread
>> can then start consuming them. Without this notification, the iothread
>> only polls for free buffers when it times out or gets woken up
>> otherwise.
>>    
>
> When you say, polls for free buffers, what do you mean by that?
>
> You mean, there's a can_read() somewhere that checks for free buffers?

Not just can_read(), in-qemu applications too can query when writes to
guests will go through.

> I think switching to qemu_set_fd_handler() would be a better solution.

Hm, there's no fd here. How to signal to apps (ports) when a guest
becomes writable?

		Amit