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Re: [Xen-devel] [PATCH] [QEMU-DM] Upgrade emulated UART to 16550A.

  • To: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
  • From: "Trolle Selander" <trolle.selander@xxxxxxxxx>
  • Date: Wed, 5 Dec 2007 15:35:22 +0100
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 05 Dec 2007 06:36:06 -0800
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I don't think they'll apply cleanly to mainline qemu due to the serial_get_token stuff, which is xen-specific, but it should be utterly trivial to fix this. I'll make new patches against the latest mainline qemu and submit them to qemu-devel as soon as I have time. I don't think qemu will benefit as much from them performance-wise, but they definitely do belong upstream.

On Dec 5, 2007 3:24 PM, Daniel P. Berrange <berrange@xxxxxxxxxx> wrote:
On Tue, Dec 04, 2007 at 05:32:39PM +0100, Trolle Selander wrote:
> This patch adds 16550 emulation to qemu-dm. I still consider it a work in
> progress, but from my testing, it consistently performs better than the old
> code already, sometimes considerably so (on my laptop, dumping out data over
> serial from a HVM DomU -> pty in Dom0 was up to 5.3 times faster than with
> the old 16450 code). I can consistenly reach full 115200 baud speeds over
> physical serial lines when the virtual device is backed by a phys port,
> which I never could with the old code.
> There are still some things to be done. I want to add proper error handling,
> so that overflow/framing & parity errors on the physical port get detected
> and reported by the virtual port. Also, now that FIFOs are in place, I
> believe performance could be improved significantly by putting some code
> into the hypervisor so that reads & writes from the FIFOs don't have to exit
> into qemu-dm at all. I'm also reading up on the specs for newer uarts with
> deeper FIFOs.
> However, for now, I think this patch is already quite good, and I don't
> think I should sit on it any longer. I'm looking forward to hearing what
> results others will get with it.

From a quick glance through the patches there doesn't appear to be anything
that is Xen specific in these patches. If I am correct in this understanding,
could you send the patches to upstream qemu-devel mailing lists, so Xen does
not have to carry this fork forever.

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