Messages in this thread | | | Date | Sun, 25 Jun 2006 14:32:32 +0800 | From | Fengguang Wu <> | Subject | Re: [PATCH 7/7] iosched: introduce deadline_kick_page() |
| |
On Sat, Jun 24, 2006 at 01:01:04PM +0200, Jens Axboe wrote: > > /* > > + * We have a pending read on @page, > > + * find the corresponding request of type READA, > > + * promote it to READ, and reschedule it. > > + */ > > +static int > > +deadline_kick_page(struct request_queue *q, struct page *page) > > +{ > > + struct deadline_data *dd = q->elevator->elevator_data; > > + struct deadline_rq *drq; > > + struct request *rq; > > + struct list_head *pos; > > + struct bio_vec *bvec; > > + struct bio *bio; > > + int i; > > + > > + list_for_each(pos, &dd->fifo_list[READ]) { > > + drq = list_entry_fifo(pos); > > + rq = drq->request; > > + if (rq->flags & (1 << BIO_RW_AHEAD)) { > > + rq_for_each_bio(bio, rq) { > > + bio_for_each_segment(bvec, bio, i) { > > + if (page == bvec->bv_page) > > + goto found; > > + } > > + } > > + } > > + } > > Uh that's horrible! > > Before we go into further details, I'd like to see some numbers on where > this makes a difference.
Sorry, it is. It brings non-trivial overhead.
This is the oprofile outputs:
reading small files: 1245 c01edae4 9 0.1404 deadline_dispatch_requests 1253 c01ed4d6 9 0.1404 deadline_queue_empty 1338 c01ed3d5 8 0.1248 deadline_kick_page 1619 c01ed350 6 0.0936 deadline_add_drq_fifo 1707 c01eda62 5 0.0780 deadline_add_request 1712 c01ed2e5 5 0.0780 deadline_set_request 1867 c01ed871 4 0.0624 deadline_remove_request 2242 c01ed9b9 2 0.0312 deadline_add_drq_rb 2244 c01edc1e 2 0.0312 deadline_merge 2246 c01ed923 2 0.0312 deadline_move_request 2249 c01ed232 2 0.0312 deadline_put_request
reading a big file: 1330 c01ed3d5 89 0.2926 deadline_kick_page 2528 c01edae4 16 0.0526 deadline_dispatch_requests 3036 c01ed9b9 8 0.0263 deadline_add_drq_rb 3163 c01ed4d6 7 0.0230 deadline_queue_empty 3394 c01edc1e 5 0.0164 deadline_merge 3399 c01ed923 5 0.0164 deadline_move_request 3403 c01ed2e5 5 0.0164 deadline_set_request 3707 c01eda62 3 0.0099 deadline_add_request 3711 c01ed871 3 0.0099 deadline_remove_request 3917 c01ede3c 2 0.0066 deadline_merged_request 3920 c01ed232 2 0.0066 deadline_put_request 4214 c01ed350 1 0.0033 deadline_add_drq_fifo
The overhead of deadline_kick_page() becomes large when the request is large (256 pages). But I guess there's way to optimize it: - most requests will be consisted of a set of continuous pages, i.e. a range comparison will be sufficient. - for a system with lots of queued requests(>100), maybe the gain can well pay for the overheads?
btw, some mails for this patchset did not return to me, perhaps my mail system was broken after a previous crash... Sorry, I'll resend them soon.
Thanks, Wu - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |