On Wed, Mar 20, 2013 at 03:56:33PM +0100, Benoît Canet wrote:
> > But I don't understand why bs->slice_time is modified instead of keeping
> > it constant at 100 ms:
> >
> > bs->slice_time = wait_time * BLOCK_IO_SLICE_TIME * 10;
> > bs->slice_end += bs->slice_time - 3 * BLOCK_IO_SLICE_TIME;
> > if (wait) {
> > *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> > }
>
> In bdrv_exceed_bps_limits there is an equivalent to this with a comment.
>
> ---------
> /* When the I/O rate at runtime exceeds the limits,
> * bs->slice_end need to be extended in order that the current statistic
> * info can be kept until the timer fire, so it is increased and tuned
> * based on the result of experiment.
> */
> bs->slice_time = wait_time * BLOCK_IO_SLICE_TIME * 10;
> bs->slice_end += bs->slice_time - 3 * BLOCK_IO_SLICE_TIME;
> if (wait) {
> *wait = wait_time * BLOCK_IO_SLICE_TIME * 10;
> }
> ----------
The comment explains why slice_end needs to be extended, but not why
bs->slice_time should be changed (except that it was tuned as the result
of an experiment).
Zhi Yong: Do you remember a reason for modifying bs->slice_time?
Stefan
