Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941712AbcLWKMt (ORCPT ); Fri, 23 Dec 2016 05:12:49 -0500 Received: from mail-wm0-f49.google.com ([74.125.82.49]:35699 "EHLO mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754461AbcLWKMq (ORCPT ); Fri, 23 Dec 2016 05:12:46 -0500 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: [PATCH 6/8] blk-mq-sched: add framework for MQ capable IO schedulers From: Paolo Valente In-Reply-To: <9936D33B-AE98-46DF-B1DA-D54142A338FD@linaro.org> Date: Fri, 23 Dec 2016 11:12:41 +0100 Cc: Jens Axboe , Jens Axboe , linux-block@vger.kernel.org, Linux-Kernal , osandov@fb.com Message-Id: <1C5DEA9B-BF5D-45E6-90E0-702D5B9F7E55@linaro.org> References: <1481933536-12844-1-git-send-email-axboe@fb.com> <1481933536-12844-7-git-send-email-axboe@fb.com> <9936D33B-AE98-46DF-B1DA-D54142A338FD@linaro.org> To: Paolo Valente X-Mailer: Apple Mail (2.3124) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id uBNACrNK022931 Content-Length: 2634 Lines: 74 > Il giorno 22 dic 2016, alle ore 10:59, Paolo Valente ha scritto: > >> >> Il giorno 17 dic 2016, alle ore 01:12, Jens Axboe ha scritto: >> >> This adds a set of hooks that intercepts the blk-mq path of >> allocating/inserting/issuing/completing requests, allowing >> us to develop a scheduler within that framework. >> >> We reuse the existing elevator scheduler API on the registration >> side, but augment that with the scheduler flagging support for >> the blk-mq interfce, and with a separate set of ops hooks for MQ >> devices. >> >> Schedulers can opt in to using shadow requests. Shadow requests >> are internal requests that the scheduler uses for for the allocate >> and insert part, which are then mapped to a real driver request >> at dispatch time. This is needed to separate the device queue depth >> from the pool of requests that the scheduler has to work with. >> >> Signed-off-by: Jens Axboe >> > ... > >> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c >> new file mode 100644 >> index 000000000000..b7e1839d4785 >> --- /dev/null >> +++ b/block/blk-mq-sched.c > >> ... >> +static inline bool >> +blk_mq_sched_allow_merge(struct request_queue *q, struct request *rq, >> + struct bio *bio) >> +{ >> + struct elevator_queue *e = q->elevator; >> + >> + if (e && e->type->ops.mq.allow_merge) >> + return e->type->ops.mq.allow_merge(q, rq, bio); >> + >> + return true; >> +} >> + > > Something does not seem to add up here: > e->type->ops.mq.allow_merge may be called only in > blk_mq_sched_allow_merge, which, in its turn, may be called only in > blk_mq_attempt_merge, which, finally, may be called only in > blk_mq_merge_queue_io. Yet the latter may be called only if there is > no elevator (line 1399 and 1507 in blk-mq.c). > > Therefore, e->type->ops.mq.allow_merge can never be called, both if > there is and if there is not an elevator. Be patient if I'm missing > something huge, but I thought it was worth reporting this. > Jens, I forgot to add that I'm willing (and would be happy) to propose a fix to this, and possibly the other problems too, on my own. Just, I'm not yet expert enough to do it with having first received some feedback or instructions from you. In this specific case, I don't even know yet whether this is really a bug. Thanks, and merry Christmas if we don't get in touch before, Paolo > Paolo > > -- > To unsubscribe from this list: send the line "unsubscribe linux-block" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html