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

[Marcelo Tosatti <mtosatti@redhat.com>]

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 <mtosatti@redhat.com> 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.
> >
> >