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Re: [Qemu-devel] [PATCH v2 23/25] console: make screendump async

From: Marc-André Lureau
Subject: Re: [Qemu-devel] [PATCH v2 23/25] console: make screendump async
Date: Mon, 23 Jan 2017 12:35:03 +0000


On Mon, Jan 23, 2017 at 4:04 PM Gerd Hoffmann <address@hidden> wrote:

>   Hi,
> >
> > If you only ref, you could have the image being modified while it is
> > being saved asynchronously, this could result in tearing artefacts,
> > no?
> Yes, but you have that problem _anyway_.  screendump qmp command can run
> in parallel to guest vcpu, so it can race with guest display updates
> today.  Assuming they happen as simple framebuffer writes and therefore
> don't involve vmexit + grabbing big qemu lock.

Agreed, fwiw, I implemented a coroutine-based ppm_save in the qapi-async

btw, is it supported to reenter the main_loop in hmp_screendump_sync()

(the alternative is probably to block hmp until the async command is
finished. This would eventually be interesting if more qmp commands used
from hmp are converted to be async)
Marc-André Lureau

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