Re: [Qemu-devel] [PATCH V4 3/5] block: Enable the new throttling code in the block layer.

[Paolo Bonzini]

Il 08/08/2013 16:29, Benoît Canet ha scritto:
> tip: Do not ever use the cfg scheduler in the guest with this code.
>      It gives incorrect throttling.

This is not really accurate; the cfq scheduler reorders reads and writes
to have longer bursts, and these sometimes exceed the rate you set.  I
understood this is mostly for separate rd/wr settings, or did you
reproduce it with "total" rates too?

Also, it would be better to have a workaround for this.  Perhaps we
could simply make the default value of max nonzero?  In the old
throttling code the slice time is 0.1s, so perhaps we could see what
happens with max=0.1*avg.

Paolo