From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hare@suse.de" <hare@suse.de>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"axboe@fb.com" <axboe@fb.com>
Cc: "osandov@osandov.com" <osandov@osandov.com>
Subject: Re: [PATCH 08/10] blk-mq-sched: add framework for MQ capable IO schedulers
Date: Fri, 13 Jan 2017 16:39:21 +0000 [thread overview]
Message-ID: <1484325542.2679.3.camel@sandisk.com> (raw)
In-Reply-To: <a4c0edfa-7cb1-2b0d-141d-2ea9e0fb07ca@suse.de>
On Fri, 2017-01-13 at 12:15 +0100, Hannes Reinecke wrote:
> On 01/11/2017 10:40 PM, Jens Axboe wrote:
> > 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.
> >
> > We split driver and scheduler tags, so we can run the scheduling
> > independent of device queue depth.
> >
> > Signed-off-by: Jens Axboe <axboe@fb.com>
>
> [ .. ]
> > @@ -823,6 +847,35 @@ static inline unsigned int queued_to_index(unsigned int queued)
> > return min(BLK_MQ_MAX_DISPATCH_ORDER - 1, ilog2(queued) + 1);
> > }
> >
> > +static bool blk_mq_get_driver_tag(struct request *rq,
> > + struct blk_mq_hw_ctx **hctx, bool wait)
> > +{
> > + struct blk_mq_alloc_data data = {
> > + .q = rq->q,
> > + .ctx = rq->mq_ctx,
> > + .hctx = blk_mq_map_queue(rq->q, rq->mq_ctx->cpu),
> > + .flags = wait ? 0 : BLK_MQ_REQ_NOWAIT,
> > + };
> > +
> > + if (blk_mq_hctx_stopped(data.hctx))
> > + return false;
> > +
> > + if (rq->tag != -1) {
> > +done:
> > + if (hctx)
> > + *hctx = data.hctx;
> > + return true;
> > + }
> > +
> > + rq->tag = blk_mq_get_tag(&data);
> > + if (rq->tag >= 0) {
> > + data.hctx->tags->rqs[rq->tag] = rq;
> > + goto done;
> > + }
> > +
> > + return false;
> > +}
> > +
>
> What happens with the existing request at 'rqs[rq->tag]' ?
> Surely there is one already, right?
> Things like '->init_request' assume a fully populated array, so moving
> one entry to another location is ... interesting.
>
> I would have thought we need to do a request cloning here,
> otherwise this would introduce a memory leak, right?
> (Not to mention a potential double completion, as the request is now at
> two positions in the array)
Hello Hannes,
Have you noticed that there are two .rqs[] arrays - tags->rqs and
sched_tags->rqs[]? .init_request() loops over sched_tags->rqs[]. The
above assignment applies to tags->rqs[].
Bart.
next prev parent reply other threads:[~2017-01-13 16:39 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-11 21:39 [PATCHSET v6] blk-mq scheduling framework Jens Axboe
2017-01-11 21:39 ` [PATCH 01/10] block: move existing elevator ops to union Jens Axboe
2017-01-12 10:15 ` Johannes Thumshirn
2017-01-12 21:17 ` Bart Van Assche
2017-01-13 8:34 ` Christoph Hellwig
2017-01-13 15:00 ` Jens Axboe
2017-01-11 21:39 ` [PATCH 02/10] blk-mq: make mq_ops a const pointer Jens Axboe
2017-01-12 10:14 ` Johannes Thumshirn
2017-01-13 8:16 ` Christoph Hellwig
2017-01-11 21:39 ` [PATCH 03/10] block: move rq_ioc() to blk.h Jens Axboe
2017-01-12 10:14 ` Johannes Thumshirn
2017-01-12 21:18 ` Bart Van Assche
2017-01-13 8:33 ` Christoph Hellwig
2017-01-11 21:39 ` [PATCH 04/10] blk-mq: un-export blk_mq_free_hctx_request() Jens Axboe
2017-01-12 10:13 ` Johannes Thumshirn
2017-01-12 21:18 ` Bart Van Assche
2017-01-13 8:16 ` Christoph Hellwig
2017-01-11 21:39 ` [PATCH 05/10] blk-mq: export some helpers we need to the scheduling framework Jens Axboe
2017-01-12 10:17 ` Johannes Thumshirn
2017-01-12 21:20 ` Bart Van Assche
2017-01-13 8:17 ` Christoph Hellwig
2017-01-13 15:01 ` Jens Axboe
2017-01-11 21:39 ` [PATCH 06/10] blk-mq-tag: cleanup the normal/reserved tag allocation Jens Axboe
2017-01-12 21:22 ` Bart Van Assche
2017-01-12 22:07 ` Jens Axboe
2017-01-13 8:30 ` Christoph Hellwig
2017-01-13 15:06 ` Jens Axboe
2017-01-11 21:40 ` [PATCH 07/10] blk-mq: abstract out helpers for allocating/freeing tag maps Jens Axboe
2017-01-12 21:29 ` Bart Van Assche
2017-01-12 21:54 ` Jens Axboe
2017-01-13 8:25 ` Johannes Thumshirn
2017-01-11 21:40 ` [PATCH 08/10] blk-mq-sched: add framework for MQ capable IO schedulers Jens Axboe
2017-01-12 21:45 ` Bart Van Assche
2017-01-12 21:59 ` Jens Axboe
2017-01-13 11:15 ` Hannes Reinecke
2017-01-13 16:39 ` Bart Van Assche [this message]
2017-01-13 16:41 ` Omar Sandoval
2017-01-13 17:43 ` Hannes Reinecke
2017-01-11 21:40 ` [PATCH 09/10] mq-deadline: add blk-mq adaptation of the deadline IO scheduler Jens Axboe
2017-01-12 21:53 ` Bart Van Assche
2017-01-11 21:40 ` [PATCH 10/10] blk-mq-sched: allow setting of default " Jens Axboe
2017-01-12 21:54 ` Bart Van Assche
2017-01-12 21:16 ` [PATCHSET v6] blk-mq scheduling framework Bart Van Assche
2017-01-13 8:15 ` Hannes Reinecke
2017-01-13 11:04 ` Hannes Reinecke
2017-01-13 12:10 ` Hannes Reinecke
2017-01-13 15:05 ` Jens Axboe
2017-01-13 15:03 ` Jens Axboe
2017-01-13 15:23 ` Jens Axboe
2017-01-13 15:33 ` Hannes Reinecke
2017-01-13 15:34 ` Jens Axboe
2017-01-13 15:59 ` Hannes Reinecke
2017-01-13 16:00 ` Jens Axboe
2017-01-13 16:02 ` Jens Axboe
2017-01-13 21:45 ` Jens Axboe
2017-01-16 8:11 ` Hannes Reinecke
2017-01-16 15:12 ` Jens Axboe
2017-01-16 15:16 ` Jens Axboe
2017-01-16 15:47 ` Jens Axboe
2017-01-13 10:09 ` Hannes Reinecke
2017-01-15 10:12 ` Paolo Valente
2017-01-15 15:55 ` Jens Axboe
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