Re: [Qemu-devel] [PATCH 2/2] qxl: add QXL_IO_UPDATE_MEM for guest S3&S4 support

[yhalperi <yhalperi@redhat.com>]

On 06/26/2011 08:47 PM, Alon Levy wrote:
> On Sun, Jun 26, 2011 at 12:59:06PM -0400, Yonit Halperin wrote:
>> Sorry for the late response, wasn't available.
>> I'm afraid  that (1) and (2) will indeed wakeup the worker, but will not assure emptying the command ring, as it depends on the client pipe size.
>>
>
> I actually can't figure out what wakeup does (that's what both NOTIFY and
> NOTIFY_CURSOR do, see hw/qxl.c).
It turns on an event the worker is waiting for on epoll_wait.

What we did in prepare_to_sleep before was
> call flush_all_qxl_commands, which reads the command and cursor rings until
> they are empty (calling flush_cursor_commands and flush_display_commands), waiting
> whenever the pipe is too large. (avoiding this wait still needs to be done, but
> after ensuring suspend is correct).
>
> More to the point this flush is done from handle_dev_destroy_surfaces, but
> this is not good enough since this also destroys the surfaces, before we have
> a chance to actually render the surfaces.
>
> Perhaps RED_WORKER_MESSAGE_STOP should do a flush_all_qxl_commands?
>
We can do it as long as it doesn't affect migration - does STOP happens 
before or after savevm? If it happens after - we can't touch the command 
ring, i.e., we can't call flush. And even if it happens before - do we 
really want to call flush during migration and presumably slow it down?

Cheers,
Yonit.

>>
>> ----- Original Message -----
>> From: "Alon Levy"<alevy@redhat.com>
>> To: "Gerd Hoffmann"<kraxel@redhat.com>
>> Cc: qemu-devel@nongnu.org, yhalperi@redhat.com
>> Sent: Wednesday, June 22, 2011 11:57:54 AM
>> Subject: Re: [Qemu-devel] [PATCH 2/2] qxl: add QXL_IO_UPDATE_MEM for guest S3&S4 support
>>
>> On Wed, Jun 22, 2011 at 11:13:19AM +0200, Gerd Hoffmann wrote:
>>>    Hi,
>>>
>>>>> worker call.  We can add a I/O command to ask qxl to push the
>>>>> release queue head to the release ring.
>>>>
>>>> So you suggest to replace QXL_IO_UPDATE_MEM with what, two io commands instead
>>>> of using the val parameter?
>>>
>>> I'd like to (a) avoid updating the libspice-server API if possible
>>> and (b) have one I/O command for each logical step.  So going into
>>> S3 could look like this:
>>>
>>>    (0) stop putting new commands into the rings
>>>    (1) QXL_IO_NOTIFY_CMD
>>>    (2) QXL_IO_NOTIFY_CURSOR
>>>        qxl calls notify(), to make the worker thread empty the command
>>>        rings before it processes the next dispatcher request.
>>>    (3) QXl_IO_FLUSH_SURFACES (to be implemented)
>>>        qxl calls stop()+start(), spice-server renders all surfaces,
>>>        thereby flushing state to device memory.
>>>    (4) QXL_IO_DESTROY_ALL_SURFACES
>>>        zap surfaces
>>>    (5) QXL_IO_FLUSH_RELEASE (to be implemented)
>>>        push release queue head into the release ring, so the guest
>>>        will see it and can release everything.
>>>
>>> (1)+(2)+(4) exist already.
>>> (3)+(5) can be done without libspice-server changes.
>>>
>>> Looks workable?
>>
>> yeah. Yonit?
>>
>>>
>>> cheers,
>>>    Gerd
>>>
>>>
>>