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

[Troy Benjegerdes]

On Wed, Oct 05, 2005 at 03:27:18PM +0400, Brad Campbell wrote:
> 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).

What network do you have between the client and nfs server? Also, what
throughput do you see to the NFS server? (and what are the nfs 'wsize'
and 'rsize' settings)

> *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).

Does the stall still happen if you don't ping the guest?