From: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
Christoph Hellwig <hch@lst.de>
Cc: "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Sagi Grimberg <sagi@grimberg.me>,
Bart Van Assche <bvanassche@acm.org>
Subject: Re: [RFC PATCH] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING
Date: Wed, 29 Jul 2020 11:20:48 +0000 [thread overview]
Message-ID: <SN4PR0401MB35980A2B94FFAC8272BD076A9B700@SN4PR0401MB3598.namprd04.prod.outlook.com> (raw)
In-Reply-To: 20200728134938.1505467-1-ming.lei@redhat.com
On 28/07/2020 15:50, Ming Lei wrote:
[...]
> -static void hctx_lock(struct blk_mq_hw_ctx *hctx, int *srcu_idx)
> - __acquires(hctx->srcu)
> +static void hctx_lock(struct blk_mq_hw_ctx *hctx)
> {
> - if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
> - /* shut up gcc false positive */
> - *srcu_idx = 0;
> + if (!(hctx->flags & BLK_MQ_F_BLOCKING))
> rcu_read_lock();
> - } else
> - *srcu_idx = srcu_read_lock(hctx->srcu);
> + else
> + percpu_ref_get(&hctx->queue->dispatch_counter);
> }
I quite like this because it hides the internals of hctx_lock() (rcu vs srcu)
from the callers.
> /**
> @@ -1486,8 +1479,6 @@ bool blk_mq_dispatch_rq_list(struct blk_mq_hw_ctx *hctx, struct list_head *list,
> */
> static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
> {
> - int srcu_idx;
> -
> /*
> * We should be running this queue from one of the CPUs that
> * are mapped to it.
> @@ -1521,9 +1512,9 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
>
> might_sleep_if(hctx->flags & BLK_MQ_F_BLOCKING);
>
> - hctx_lock(hctx, &srcu_idx);
> + hctx_lock(hctx);
> blk_mq_sched_dispatch_requests(hctx);
> - hctx_unlock(hctx, srcu_idx);
> + hctx_unlock(hctx);
blk_mq_sched_dispatch_requests also has this comment at the beginning:
/* RCU or SRCU read lock is needed before checking quiesced flag */
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
I think the SRCU part needs to be changed to percpu_ref or the whole comment
should probably just mention the hctx_lock().
next prev parent reply other threads:[~2020-07-29 11:20 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-28 13:49 [RFC PATCH] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING Ming Lei
2020-07-29 10:28 ` Ming Lei
2020-07-29 15:42 ` Sagi Grimberg
2020-07-29 15:49 ` Ming Lei
2020-07-29 22:37 ` Sagi Grimberg
2020-07-30 14:53 ` Ming Lei
2020-07-30 16:10 ` Sagi Grimberg
2020-07-30 18:18 ` Keith Busch
2020-07-30 18:23 ` Sagi Grimberg
2020-07-30 19:27 ` Keith Busch
2020-07-30 19:53 ` Jens Axboe
2020-07-30 21:03 ` Sagi Grimberg
2020-07-31 0:33 ` Ming Lei
2020-07-31 0:24 ` Ming Lei
2020-07-31 0:28 ` Ming Lei
2020-07-29 11:20 ` Johannes Thumshirn [this message]
2020-07-29 16:12 ` Keith Busch
2020-07-29 22:16 ` Ming Lei
2020-07-29 22:42 ` Sagi Grimberg
2020-07-30 15:05 ` Ming Lei
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