Re: [Qemu-devel] [patch] non-blocking disk IO

[Brad Campbell]

John Coiner wrote:

> Thanks for the report. I was able to reproduce this.
>
> The problem was due to missing Makefile dependencies. The patch modifies 
> 'block_int.h', which is #included in several '.c' files. The file 
> 'block.c' recompiled at 'make' time, but 'block-qcow.c' didn't. The 
> resulting '.o' files had different opinions about what a 
> BlockDriverState struct looked like, which broke the qcow code.

Having had it running for a while I did some performance tests and found no performance gains _at 
all_, but then I'm running my entire system over the network on an NFS filesystem (this machine has 
no disks in it).

*NOW* having said that, one of the tricks I do to keep qemu from "going to sleep" when running a 
long process like a big software install (sometimes it appears to stall until I move the mouse 
around a bit) is to ping the machine constantly from the host.
Prior to this patch I would get pings that varied from 1ms to 250ms. With this patch I get a spread 
from about 1ms to 15ms tops. So it has smoothed out the operation of the host noticably (also 
noticable in screen redraws and UI responsiveness while under a heavy disk load).

No performance for me, but it just "feels" better to use all round.

So, no functional regressions, better usability but no performance here (probably due to running the 
whole thing over nfs)
One day I'll get a local disk and test it out.

As a lark, I also did a fresh compile of the BOCHS latest CVS bios with the apm and dma patches 
included. It appears to give me a slight speed improvement on booting my XP guest, but given the 
nature of my system that could be statistical noise.. If anyone wants to give it a whirl I have put 
my newly compiled bios here http://fnarfbargle.dyndns.org:81/bios

Regards,
Brad
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