From: Hannes Reinecke <hare@suse.de>
To: Omar Sandoval <osandov@osandov.com>
Cc: Jens Axboe <axboe@fb.com>,
linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
bart.vanassche@sandisk.com
Subject: Re: [PATCH 08/10] blk-mq-sched: add framework for MQ capable IO schedulers
Date: Fri, 13 Jan 2017 18:43:41 +0100 [thread overview]
Message-ID: <9d76b1ce-34c5-d3e2-085e-1d78d6c2fa44@suse.de> (raw)
In-Reply-To: <20170113164153.GA15751@vader>
On 01/13/2017 05:41 PM, Omar Sandoval wrote:
> On Fri, Jan 13, 2017 at 12:15:17PM +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)
>>
>> Cheers,
>>
>> Hannes
>
> The entries in tags->rqs aren't slab objects, they're pointers into
> pages allocated separately and tracked on tags->page_list. See
> blk_mq_alloc_rqs(). In blk_mq_free_rqs(), we free all of the pages on
> tags->page_list, so there shouldn't be a memory leak.
>
> As for hctx->tags->rqs, entries are only overwritten when a scheduler is
> enabled. In that case, the rqs array is storing pointers to requests
> actually from hctx->sched_tags, so overwriting/leaking isn't an issue.
Ah. Thanks.
That explains it.
Cheers,
Hannes
--
Dr. Hannes Reinecke zSeries & Storage
hare@suse.de +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
next prev parent reply other threads:[~2017-01-13 17:43 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
2017-01-13 16:41 ` Omar Sandoval
2017-01-13 17:43 ` Hannes Reinecke [this message]
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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