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Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async
From: |
Alon Levy |
Subject: |
Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async |
Date: |
Tue, 6 Mar 2012 16:23:09 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Tue, Mar 06, 2012 at 10:53:42AM -0300, Luiz Capitulino wrote:
> On Tue, 06 Mar 2012 07:51:29 -0600
> Anthony Liguori <address@hidden> wrote:
>
> > On 03/06/2012 07:16 AM, Alon Levy wrote:
> > > On Tue, Mar 06, 2012 at 09:24:27AM -0300, Luiz Capitulino wrote:
> > >> On Tue, 06 Mar 2012 08:36:34 +0100
> > >> Gerd Hoffmann<address@hidden> wrote:
> > >>
> > >>> Hi,
> > >>>
> > >>>>> How would the parallel execution facility be opaque to the
> > >>>>> implementer?
> > >>>>> screendump returns, screendump_async needs to pass a closure. You can
> > >>>>> automatically generate any amount of code, but you can only have a
> > >>>>> single function implementation with longjmp/coroutine, or having a
> > >>>>> saparate thread per command but that would mean taking locks for
> > >>>>> anything not trivial, which avoids the no-change-to-implementation. Is
> > >>>>> this what you have in mind?
> > >>>>
> > >>>> It would not be opaque to the implementer. But it would avoid
> > >>>> introducing new commands and events, instead we have a unified
> > >>>> mechanism
> > >>>> to signal completion.
> > >>>
> > >>> Ok. We have a async mechanism today: .mhandler.cmd_async = ...
> > >>>
> > >>> I know it has its problems like no cancelation and is deprecated and
> > >>> all. But still: how about using it as interim until QAPI-based async
> > >>> monitor support is ready? We could unbreak qxl screendumps without
> > >>> having to introduce a new (but temporary!) screendump_async command +
> > >>> completion event.
> > >>
> > >> There are a few problems here, but the blocking one is that a command
> > >> can't go from sync to async. This is an incompatible change.
> > >>
> > >> If you mind adding the temporary command and if this issue is so rare
> > >> that none can reproduce it, then I'd suggest to wait for 1.2.
> > >>
> > >
> > > There are two options really:
> > > 1. revert the patches that changed qxl screendump to save the ppm
> > > before (possibly) updating the framebuffer.
> > > 2. introduce a new command that is really async
> > >
> > > The third option, what Gerd proposes, doesn't break the blocking chain
> > > going from the A, the dual purpose spice client and libvirt client,
> > > through libvirt, qemu, spice and back to A.
> > >
> > > If no one can reproduce the block then it would seem 1 makes sense.
> >
> > So let's start with a reproducible test case that demonstrates the problem
> > before we start introducing new commands then if there's doubt about the
> > nature
> > of the problem.
>
> Completely agree, I was going to suggest that too.
>
So cutting off a part of the email is a good way to win arguments? cool
trick. I agree a reproducer is a good idea, but as I mentioned in the
cut part, doing the update area without keeping the monitor waiting
improves performance of the guest by letting it do io exits. Why is that
a bad thing?
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, (continued)
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Luiz Capitulino, 2012/03/05
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Gerd Hoffmann, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Gerd Hoffmann, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Luiz Capitulino, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Anthony Liguori, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Luiz Capitulino, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async,
Alon Levy <=
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Anthony Liguori, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Anthony Liguori, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Alon Levy, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Anthony Liguori, 2012/03/06
- Re: [Qemu-devel] [PATCH v2 1/2] console: add hw_screen_dump_async, Gerd Hoffmann, 2012/03/07