Re: [Qemu-devel] [PATCH v8 3/4] block: add block timer and throttling algorithm

[Marcelo Tosatti]

On Tue, Sep 13, 2011 at 11:09:46AM +0800, Zhi Yong Wu wrote:
> On Fri, Sep 9, 2011 at 10:44 PM, Marcelo Tosatti <address@hidden> wrote:
> > On Thu, Sep 08, 2011 at 06:11:07PM +0800, Zhi Yong Wu wrote:
> >> Note:
> >>      1.) When bps/iops limits are specified to a small value such as 511 
> >> bytes/s, this VM will hang up. We are considering how to handle this 
> >> senario.
> >
> > You can increase the length of the slice, if the request is larger than
> > slice_time * bps_limit.
> Yeah, but it is a challenge for how to increase it. Do you have some nice 
> idea?

If the queue is empty, and the request being processed does not fit the
queue, increase the slice so that the request fits.

That is, make BLOCK_IO_SLICE_TIME dynamic and adjust it as described
above (if the bps or io limits change, reset it to the default
BLOCK_IO_SLICE_TIME).

> >>      2.) When "dd" command is issued in guest, if its option bs is set to 
> >> a large value such as "bs=1024K", the result speed will slightly bigger 
> >> than the limits.
> >
> > Why?
> This issue has not existed. I will remove it.
> When drive bps=1000000, i did some testings on guest VM.
> 1.) bs=1024K
> 18+0 records in
> 18+0 records out
> 18874368 bytes (19 MB) copied, 26.6268 s, 709 kB/s
> 2.) bs=2048K
> 18+0 records in
> 18+0 records out
> 37748736 bytes (38 MB) copied, 46.5336 s, 811 kB/s
> 
> >
> > There is lots of debugging leftovers in the patch.
> sorry, i forgot to remove them.
> >
> >