Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751884Ab3JTMOo (ORCPT ); Sun, 20 Oct 2013 08:14:44 -0400 Received: from mail-pb0-f48.google.com ([209.85.160.48]:38370 "EHLO mail-pb0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751786Ab3JTMOf (ORCPT ); Sun, 20 Oct 2013 08:14:35 -0400 From: Hong Zhiguo To: tj@kernel.org, vgoyal@redhat.com Cc: cgroups@vger.kernel.org, axboe@kernel.dk, linux-kernel@vger.kernel.org, Hong Zhiguo Subject: [PATCH v4 2/2] blk-throttle: trim tokens generated for an idle tree Date: Sun, 20 Oct 2013 20:11:12 +0800 Message-Id: <1382271072-15664-3-git-send-email-zhiguohong@tencent.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1382271072-15664-1-git-send-email-zhiguohong@tencent.com> References: <20131018155532.GD2277@redhat.com> <1382271072-15664-1-git-send-email-zhiguohong@tencent.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4105 Lines: 127 From: Hong Zhiguo Why ==== Pointed out by Vivek: Tokens generated during idle period should be trimmed. Otherwise a huge bio may be permited immediately. Overlimit behaviour may be observed during short I/O throughput test. Vivek also pointed out: We should not over-trim for hierarchical groups. Suppose a subtree of groups are idle when a big bio comes. The token of the child group is trimmed and not enough. So the bio is queued on the child group. After some jiffies the child group reserved enough tokens and the bio climbs up. If we trim the parent group at this time again, this bio will wait too much time than expected. Analysis ======== When the bio is queued on child group, all it's ancestor groups becomes non-idle. They should start to reserve tokens for that bio from this moment. And their reserved tokens before should be trimmed at this moment. How ==== service_queue now has a new member nr_queued_tree[2], to represent the the number of bios waiting on the subtree rooted by this sq. When a bio is queued on the hierarchy first time, nr_queued_tree of all ancestors and the child group itself are increased. When a bio climbs up, nr_queued_tree of the child group is decreased. When nr_queued_tree turns from zero to one, the tokens reserved before are trimmed. And after this switch, this group will never be trimmed to reserve tokens for the bio waiting on it's descendant group. Signed-off-by: Hong Zhiguo --- block/blk-throttle.c | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 45d4d91..d10a5e1 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -63,6 +63,10 @@ struct throtl_service_queue { */ struct list_head queued[2]; /* throtl_qnode [READ/WRITE] */ unsigned int nr_queued[2]; /* number of queued bios */ + /* + * number of bios queued on this subtree + */ + unsigned int nr_queued_tree[2]; /* * RB tree of active children throtl_grp's, which are sorted by @@ -699,6 +703,11 @@ static void tg_update_token(struct throtl_grp *tg, bool rw) do_div(token, HZ); tg->bytes_token[rw] += token; + /* trim token if the whole subtree is idle */ + if (!tg->service_queue.nr_queued_tree[rw] && + tg->bytes_token[rw] > THROTL_BURST_BYTES) + token = THROTL_BURST_BYTES; + tg->t_c[rw] = jiffies; } @@ -843,6 +852,28 @@ static void throtl_charge_bio(struct throtl_grp *tg, struct bio *bio) } /** + * tg_update_nr_queue_tree - update nr_queued_tree of all ancestors + * @sq: the target service_queue + * + * Traverse from @sq to the top throtl_grp, increase their + * nr_queued_tree. If one sq has zero nr_queued_tree and now turns to + * one, trim the tokens generated before. From now on it will never + * get trimmed until same thing happens next time. + */ +static void tg_update_nr_queue_tree(struct throtl_service_queue *sq, bool rw) +{ + struct throtl_grp *tg; + + while (sq && (tg = sq_to_tg(sq))) { + if (!sq->nr_queued_tree[rw]) + tg_update_token(tg, rw); + + sq->nr_queued_tree[rw]++; + sq = sq->parent_sq; + } +} + +/** * throtl_add_bio_tg - add a bio to the specified throtl_grp * @bio: bio to add * @qn: qnode to use @@ -916,6 +947,9 @@ static void tg_dispatch_one_bio(struct throtl_grp *tg, bool rw) bio = throtl_pop_queued(&sq->queued[rw], &tg_to_put); sq->nr_queued[rw]--; + /* Here's the only place nr_queued_tree get decreased */ + sq->nr_queued_tree[rw]--; + throtl_charge_bio(tg, bio); /* @@ -1375,6 +1409,10 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio) bio_associate_current(bio); tg->td->nr_queued[rw]++; + + /* Here's the only place nr_queued_tree get increased */ + tg_update_nr_queue_tree(sq, rw); + throtl_add_bio_tg(bio, qn, tg); throttled = true; -- 1.8.1.2 -- 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/