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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH] opengl rendering in the sdl window |
Date: | Mon, 08 Sep 2008 21:45:18 -0500 |
User-agent: | Thunderbird 2.0.0.16 (X11/20080723) |
Jamie Lokier wrote:
Daniel P. Berrange wrote:Just thought I'd mention one other thing - it is not actually clearcut / or guarenteed that XShm + VNC would improve performance in all circumstances. This is because X pixmaps created via XShm apparently cannot live in video memory, and thus it is not so easy to get full performance advantage of hardware acceleration - this could impact scaling for example.I haven't seen any scaling with VNC so far, but it would be nice sometimes.
It's been supported in gtk-vnc for a while now.
How does sending the image over the wire then asking the server to scale it using RENDER improve on sending it over XShm then asking the server to xscale the pixel using RENDER? Or is there something else you can do when you don't use XShm?
The key point being you can avoid a copy even when using a shared memory extension because you don't necessarily have to back the shared memory with an XShmImage. Even if you have to copy from shared memory to a hardware framebuffer, you avoid copying the data to the kernel socket buffer.
But copying data isn't super expensive assuming you're hitting the cpu cache (which you probably are). So I don't know how much it saves in real life.
Regards, Anthony Liguori
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