From: Sagi Grimberg <sagi@grimberg.me>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
"Paul E. McKenney" <paulmck@kernel.org>,
linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
Chao Leng <lengchao@huawei.com>, Keith Busch <kbusch@kernel.org>,
Ming Lin <mlin@kernel.org>, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface
Date: Tue, 28 Jul 2020 02:43:06 -0700 [thread overview]
Message-ID: <6a678d5d-22b2-5238-92c5-d68e2aafeb9e@grimberg.me> (raw)
In-Reply-To: <44f07df6-3107-3e7f-ee02-7bc43293ee6b@grimberg.me>
>>>>> I like the tagset based interface. But the idea of doing a per-hctx
>>>>> allocation and wait doesn't seem very scalable.
>>>>>
>>>>> Paul, do you have any good idea for an interface that waits on
>>>>> multiple srcu heads? As far as I can tell we could just have a single
>>>>> global completion and counter, and each call_srcu would just just
>>>>> decrement it and then the final one would do the wakeup. It would
>>>>> just
>>>>> be great to figure out a way to keep the struct rcu_synchronize and
>>>>> counter on stack to avoid an allocation.
>>>>>
>>>>> But if we can't do with an on-stack object I'd much rather just embedd
>>>>> the rcu_head in the hw_ctx.
>>>>
>>>> I think we can do that, please see the following patch which is
>>>> against Sagi's V5:
>>>
>>> I don't think you can send a single rcu_head to multiple call_srcu
>>> calls.
>>
>> OK, then one variant is to put the rcu_head into blk_mq_hw_ctx, and put
>> rcu_synchronize into blk_mq_tag_set.
>
> I can cook up a spin,
Nope.. spoke too soon, the rcu_head needs to be in a context that has
access to the counter (which is what you called blk_mq_srcu_sync).
you want to add also a pointer to hctx? that is almost as big as
rcu_synchronize...
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next prev parent reply other threads:[~2020-07-28 9:43 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-27 23:10 [PATCH v5 0/2] improve nvme quiesce time for large amount of namespaces Sagi Grimberg
2020-07-27 23:10 ` [PATCH v5 1/2] blk-mq: add tagset quiesce interface Sagi Grimberg
2020-07-27 23:32 ` Keith Busch
2020-07-28 0:12 ` Sagi Grimberg
2020-07-28 1:40 ` Ming Lei
2020-07-28 1:51 ` Jens Axboe
2020-07-28 2:17 ` Ming Lei
2020-07-28 2:23 ` Jens Axboe
2020-07-28 2:28 ` Ming Lei
2020-07-28 2:32 ` Jens Axboe
2020-07-28 3:29 ` Sagi Grimberg
2020-07-28 3:25 ` Sagi Grimberg
2020-07-28 7:18 ` Christoph Hellwig
2020-07-28 7:48 ` Sagi Grimberg
2020-07-28 9:16 ` Ming Lei
2020-07-28 9:24 ` Sagi Grimberg
2020-07-28 9:33 ` Ming Lei
2020-07-28 9:37 ` Sagi Grimberg
2020-07-28 9:43 ` Sagi Grimberg [this message]
2020-07-28 10:10 ` Ming Lei
2020-07-28 10:57 ` Christoph Hellwig
2020-07-28 14:13 ` Paul E. McKenney
2020-07-28 10:58 ` Christoph Hellwig
2020-07-28 16:25 ` Sagi Grimberg
2020-07-28 13:54 ` Paul E. McKenney
2020-07-28 23:46 ` Sagi Grimberg
2020-07-29 0:31 ` Paul E. McKenney
2020-07-29 0:43 ` Sagi Grimberg
2020-07-29 0:59 ` Keith Busch
2020-07-29 4:39 ` Sagi Grimberg
2020-08-07 9:04 ` Chao Leng
2020-08-07 9:24 ` Ming Lei
2020-08-07 9:35 ` Chao Leng
2020-07-29 4:10 ` Paul E. McKenney
2020-07-29 4:37 ` Sagi Grimberg
2020-07-27 23:10 ` [PATCH v5 2/2] nvme: use blk_mq_[un]quiesce_tagset Sagi Grimberg
2020-07-28 0:54 ` Sagi Grimberg
2020-07-28 3:21 ` Chao Leng
2020-07-28 3:34 ` Sagi Grimberg
2020-07-28 3:51 ` Chao Leng
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