From: Julian Pidancet <julian.pidancet@citrix.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
Stefano Stabellini <Stefano.Stabellini@eu.citrix.com>
Subject: Re: [Qemu-devel] Re: [PATCH 5/5] linux fbdev display driver.
Date: Fri, 18 Jun 2010 13:00:25 +0100 [thread overview]
Message-ID: <4C1B5FD9.10201@citrix.com> (raw)
In-Reply-To: <4C1B2102.9000104@redhat.com>
On 06/18/2010 08:32 AM, Gerd Hoffmann wrote:
> Hi,
>
>> For some reason, the display is extremely slow when using vnc and
>> fbdev at the same time.
>
> Gotcha. Didn't notice, but it probably depends on the hardware. Very
> likely the reason is that graphic cards usually are optimized for write
> access and reads might be slow as hell. vnc must read though.
>
Access to the framebuffer are cached Write-Combining by default with fbdev, which is probably causing this latency.
One solution would be to disable the display allocator when vnc is present, and let it read from a software surface instead of reading from the framebuffer (like in your initial patch). It would probably decrease display performance, but not as much as it is now if we let the vnc driver read from the hardware framebuffer.
We can easily implement a surface usage counter in the display allocator code, so the fbdev driver can know whether or not the surface is read by other drivers at the same time.
--
Julian Pidancet
next prev parent reply other threads:[~2010-06-18 11:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-15 10:05 [Qemu-devel] [PATCH 0/5] fbdev display driver + misc bits Gerd Hoffmann
2010-06-15 10:05 ` [Qemu-devel] [PATCH 1/5] QLIST-ify display change listeners Gerd Hoffmann
2010-06-15 10:05 ` [Qemu-devel] [PATCH 2/5] add unregister_displaychangelistener Gerd Hoffmann
2010-06-15 10:05 ` [Qemu-devel] [PATCH 3/5] Fix and simplify gui timer logic Gerd Hoffmann
2010-06-15 10:05 ` [Qemu-devel] [PATCH 4/5] add pflib: PixelFormat conversion library Gerd Hoffmann
2010-06-15 10:05 ` [Qemu-devel] [PATCH 5/5] linux fbdev display driver Gerd Hoffmann
2010-06-16 12:44 ` [Qemu-devel] " Stefano Stabellini
2010-06-16 16:22 ` Julian Pidancet
2010-06-17 10:43 ` Gerd Hoffmann
2010-06-17 14:29 ` Julian Pidancet
2010-06-17 16:25 ` Julian Pidancet
2010-06-18 7:32 ` Gerd Hoffmann
2010-06-18 12:00 ` Julian Pidancet [this message]
2010-06-24 18:38 ` [Qemu-devel] [PATCH 0/5] fbdev display driver + misc bits Julian Pidancet
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