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Re: [Qemu-devel] [PATCH] A simple way to DMA (and async. IO) to make win

From: Fabrice Bellard
Subject: Re: [Qemu-devel] [PATCH] A simple way to DMA (and async. IO) to make win2003 happy
Date: Thu, 02 Feb 2006 00:29:21 +0100
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20040913

Juergen Pfennig wrote:
Hello ...

Please note: I will send the Async IO stuff later, see below.

This Patch: Here is a very simple patch to ide.c that does not change
            the controller type and that lets an existing win2003 in-
            stallation use multi-sector IO and/or DMA.
> [...]

I just merged a more complete patch from Jens Axboe. Does it give acceptable performance in win2003 ?

(3) My way to async IO is different, read below. The implementation
    does async read and write. My plans are to make the SDL async too.

(4) The async IO layer integrates well with Fabrice Bellard's IOHandlers.
    In fact vl.c needs no modifications, the code uses a pipe to signal
    that IO got ready. The modifications on the block driver layer are

To say this again: the async IO stuff itself is about 600 lines of code
(in one file) but it needs several small changes in qemu. Here are some
fake definitions that you might help you to get a first impression:

So there are two async I/O patches now :-)

I am more interested by these patches now because I want to improve the performance to match (or exceed !) the performance of the other virtualizers. I have at least 5 items on my TODO list :

1) New kqemu which virtualizes both user and kernel code (currently in alpha stage but not released yet).

2) DMA block I/O (merged)

3) async block I/O (not merged yet)

4) Network adapter using DMA (not merged yet)

5) VGA acceleration (either improve Cirrus VGA or switch back to Bochs VGA for Win 2000/XP or Linux)


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