On Thu, Oct 20 2005, Tejun Heo wrote:
> On Thu, Oct 20, 2005 at 01:21:09PM +0200, Jens Axboe wrote:
> > On Wed, Oct 19 2005, Tejun Heo wrote:
> > > 02_blk_generic-dispatch-queue-update-for-ioscheds.patch
> > >
> > > This patch updates all four ioscheds to use generic dispatch
> > > queue. There's one behavior change in as-iosched.
> > >
> > > * In as-iosched, when force dispatching
> > > (ELEVATOR_INSERT_BACK), batch_data_dir is reset to REQ_SYNC
> > > and changed_batch and new_batch are cleared to zero. This
> > > prevernts AS from doing incorrect update_write_batch after
> > > the forced dispatched requests are finished.
> > >
> > > * In cfq-iosched, cfqd->rq_in_driver currently counts the
> > > number of activated (removed) requests to determine
> > > whether queue-kicking is needed and cfq_max_depth has been
> > > reached. With generic dispatch queue, I think counting
> > > the number of dispatched requests would be more appropriate.
> > >
> > > * cfq_max_depth can be lowered to 1 again.
> >
> > I applied this one as well, with some minor changes. The biggest one is
> > a cleanup of the 'force' logic, it seems to be a little mixed up in this
> > patch. You use it for forcing dispatch, which is fine. But then it also
> > doubles as whether you want to sort insert on the generic queue or just
> > add to the tail?
>
> When forced dispatch occurs, all requests in a elevator get dumped
> into the dispatch queue. Specific elevators are free to dump in any
> order and it's likely that specific elevators don't dump in the
> optimal order - e.g. for cfq, it will dump each cfqq's in order which
> results in unnecessary seeks. That's why all the current ioscheds
> tells elv_dispatch_insert() to perform global dispatch queue sorting
> when they dump requests due to force argument. Maybe add comments to
> explain this?
But why would you ever want non-sorted dispatch adding of requests,
except for the cases where you absolutely need it to go at the back? I
don't see what dispatch forcing has to do with this at all?
--
Jens Axboe
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
