On Thursday May 10, [email protected] wrote:
>
> On May 10 2007 16:22, NeilBrown wrote:
> >
> >diff .prev/drivers/md/md.c ./drivers/md/md.c
> >--- .prev/drivers/md/md.c 2007-05-10 15:51:54.000000000 +1000
> >+++ ./drivers/md/md.c 2007-05-10 16:05:10.000000000 +1000
> >@@ -5095,7 +5095,7 @@ static int is_mddev_idle(mddev_t *mddev)
> > *
> > * Note: the following is an unsigned comparison.
> > */
> >- if ((curr_events - rdev->last_events + 4096) > 8192) {
> >+ if ((long)curr_events - (long)rdev->last_events > 4096) {
> > rdev->last_events = curr_events;
> > idle = 0;
> > }
>
> What did really change? Unless I am seriously mistaken,
>
> curr_events - last_evens + 4096 > 8192
>
> is mathematically equivalent to
>
> curr_events - last_evens > 4096
>
> The casting to (long) may however force a signed comparison which turns
> things quite upside down, and the comment does not apply anymore.
Yes, the use of a signed comparison is the significant difference.
And yes, the comment becomes wrong. I'm in the process of redrafting
that. It currently stands at:
/* sync IO will cause sync_io to increase before the disk_stats
* as sync_io is counted when a request starts, and
* disk_stats is counted when it completes.
* So resync activity will cause curr_events to be smaller than
* when there was no such activity.
* non-sync IO will cause disk_stat to increase without
* increasing sync_io so curr_events will (eventually)
* be larger than it was before. Once it becomes
* substantially larger, the test below will cause
* the array to appear non-idle, and resync will slow
* down.
* If there is a lot of outstanding resync activity when
* we set last_event to curr_events, then all that activity
* completing might cause the array to appear non-idle
* and resync will be slowed down even though there might
* not have been non-resync activity. This will only
* happen once though. 'last_events' will soon reflect
* the state where there is little or no outstanding
* resync requests, and further resync activity will
* always make curr_events less than last_events.
*
*/
Does that read at all well?
NeilBrown
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