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Date: Fri, 28 Aug 2009 12:00:08 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: Extending virtio_console to support multiple ports
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To: Amit Shah <amit.shah@redhat.com>
Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org

Amit Shah wrote:
> On (Tue) Aug 25 2009 [11:47:20], Amit Shah wrote:
>   
>> Hello all,
>>
>> Here is a new iteration of the patch series that implements a
>> transport for guest and host communications.
>>
>> The code has been updated to reuse the virtio-console device instead
>> of creating a new virtio-serial device.
>>     
>
> And the problem now is that hvc calls the put_chars function with
> spinlocks held and we now allocate pages in send_buf(), called from
> put_chars.
>   

Don't allocate pages in send_buf.  There's a fixed number of possible 
entries on the ring.  Preallocate them up front and then you don't need 
to sleep.

> A few solutions:
> - Keep things as they are, virtio_console.c remains as it is and
>   virtio_serial.c gets added
>   
Not an option from a QEMU perspective.

Regards,

Anthony Liguori