From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, John Garry <john.garry@huawei.com>,
Bart Van Assche <bvanassche@acm.org>,
Hannes Reinecke <hare@suse.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH V11 11/12] blk-mq: re-submit IO in case that hctx is inactive
Date: Thu, 14 May 2020 08:40:09 +0800 [thread overview]
Message-ID: <20200514004004.GC2073570@T590> (raw)
In-Reply-To: <20200513122147.GF6297@lst.de>
On Wed, May 13, 2020 at 02:21:47PM +0200, Christoph Hellwig wrote:
> Use of the BLK_MQ_REQ_FORCE is pretty bogus here..
>
> > + if (rq->rq_flags & RQF_PREEMPT)
> > + flags |= BLK_MQ_REQ_PREEMPT;
> > + if (reserved)
> > + flags |= BLK_MQ_REQ_RESERVED;
> > + /*
> > + * Queue freezing might be in-progress, and wait freeze can't be
> > + * done now because we have request not completed yet, so mark this
> > + * allocation as BLK_MQ_REQ_FORCE for avoiding this allocation &
> > + * freeze hung forever.
> > + */
> > + flags |= BLK_MQ_REQ_FORCE;
> > +
> > + /* avoid allocation failure by clearing NOWAIT */
> > + nrq = blk_get_request(rq->q, rq->cmd_flags & ~REQ_NOWAIT, flags);
> > + if (!nrq)
> > + return;
>
> blk_get_request returns an ERR_PTR.
>
> But I'd rather avoid the magic new BLK_MQ_REQ_FORCE hack when we can
> just open code it and document what is going on:
BLK_MQ_REQ_FORCE is actually not a hack, there are other use cases
which need that too, see commit log of patch 10/12.
>
> static struct blk_mq_tags *blk_mq_rq_tags(struct request *rq)
> {
> struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
>
> if (rq->q->elevator)
> return hctx->sched_tags;
> return hctx->tags;
> }
>
> static void blk_mq_resubmit_rq(struct request *rq)
> {
> struct blk_mq_alloc_data alloc_data = {
> .cmd_flags = rq->cmd_flags & ~REQ_NOWAIT;
> };
> struct request *nrq;
>
> if (rq->rq_flags & RQF_PREEMPT)
> alloc_data.flags |= BLK_MQ_REQ_PREEMPT;
> if (blk_mq_tag_is_reserved(blk_mq_rq_tags(rq), rq->internal_tag))
> alloc_data.flags |= BLK_MQ_REQ_RESERVED;
>
> /*
> * We must still be able to finish a resubmission due to a hotplug
> * even even if a queue freeze is in progress.
> */
> percpu_ref_get(&q->q_usage_counter);
> nrq = blk_mq_get_request(rq->q, NULL, &alloc_data);
> blk_queue_exit(q);
This way works too.
>
> if (!nrq)
> return; // XXX: warn?
It isn't possible because we clears NO_WAIT flag.
Thanks,
Ming
next prev parent reply other threads:[~2020-05-14 0:40 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 3:47 [PATCH V11 00/12] blk-mq: improvement CPU hotplug Ming Lei
2020-05-13 3:47 ` [PATCH V11 01/12] block: clone nr_integrity_segments and write_hint in blk_rq_prep_clone Ming Lei
2020-05-13 3:47 ` [PATCH V11 02/12] block: add helper for copying request Ming Lei
2020-05-13 3:47 ` [PATCH V11 03/12] blk-mq: mark blk_mq_get_driver_tag as static Ming Lei
2020-05-13 3:47 ` [PATCH V11 04/12] blk-mq: assign rq->tag in blk_mq_get_driver_tag Ming Lei
2020-05-13 3:47 ` [PATCH V11 05/12] blk-mq: add blk_mq_all_tag_iter Ming Lei
2020-05-13 11:56 ` Christoph Hellwig
2020-05-13 3:47 ` [PATCH V11 06/12] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2020-05-13 6:35 ` Hannes Reinecke
2020-05-13 11:58 ` Christoph Hellwig
2020-05-14 0:33 ` Ming Lei
2020-05-13 3:47 ` [PATCH V11 07/12] blk-mq: stop to handle IO and drain IO before hctx becomes inactive Ming Lei
2020-05-13 11:59 ` Christoph Hellwig
2020-05-14 0:36 ` Ming Lei
2020-05-14 1:12 ` Bart Van Assche
2020-05-14 3:10 ` Ming Lei
2020-05-13 3:47 ` [PATCH V11 08/12] block: add blk_end_flush_machinery Ming Lei
2020-05-13 12:00 ` Christoph Hellwig
2020-05-13 3:48 ` [PATCH V11 09/12] blk-mq: add blk_mq_hctx_handle_dead_cpu for handling cpu dead Ming Lei
2020-05-13 12:06 ` Christoph Hellwig
2020-05-13 3:48 ` [PATCH V11 10/12] block: add request allocation flag of BLK_MQ_REQ_FORCE Ming Lei
2020-05-13 10:34 ` [PATCH V12 " Ming Lei
2020-05-13 3:48 ` [PATCH V11 11/12] blk-mq: re-submit IO in case that hctx is inactive Ming Lei
2020-05-13 9:21 ` John Garry
2020-05-13 12:21 ` Christoph Hellwig
2020-05-13 15:03 ` Bart Van Assche
2020-05-14 0:45 ` Ming Lei
2020-05-14 0:40 ` Ming Lei [this message]
2020-05-13 3:48 ` [PATCH V11 12/12] block: deactivate hctx when the hctx is actually inactive Ming Lei
2020-05-13 7:34 ` [PATCH V11 00/12] blk-mq: improvement CPU hotplug John Garry
2020-05-13 10:37 ` Ming Lei
2020-05-13 11:33 ` John Garry
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