From: Chao Leng <lengchao@huawei.com>
To: Sagi Grimberg <sagi@grimberg.me>, Keith Busch <kbusch@kernel.org>
Cc: <paulmck@kernel.org>, Ming Lei <ming.lei@redhat.com>,
Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
<linux-nvme@lists.infradead.org>, <linux-block@vger.kernel.org>,
Ming Lin <mlin@kernel.org>
Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface
Date: Fri, 7 Aug 2020 17:04:38 +0800 [thread overview]
Message-ID: <31a9ba72-1322-4b7c-fb73-db0cb52989da@huawei.com> (raw)
In-Reply-To: <2f17c8ed-99f6-c71c-edd1-fd96481f432c@grimberg.me>
On 2020/7/29 12:39, Sagi Grimberg wrote:
>
>>>>> Dynamically allocating each one is possible but not very scalable.
>>>>>
>>>>> The question is if there is some way, we can do this with on-stack
>>>>> or a single on-heap rcu_head or equivalent that can achieve the same
>>>>> effect.
>>>>
>>>> If the hctx structures are guaranteed to stay put, you could count
>>>> them and then do a single allocation of an array of rcu_head structures
>>>> (or some larger structure containing an rcu_head structure, if needed).
>>>> You could then sequence through this array, consuming one rcu_head per
>>>> hctx as you processed it. Once all the callbacks had been invoked,
>>>> it would be safe to free the array.
>>>>
>>>> Sounds too simple, though. So what am I missing?
>>>
>>> We don't want higher-order allocations...
>>
>> So:
>>
>> (1) We don't want to embed the struct in the hctx because we allocate
>> so many of them that this is non-negligable to add for something we
>> typically never use.
>>
>> (2) We don't want to allocate dynamically because it's potentially
>> huge.
>>
>> As long as we're using srcu for blocking hctx's, I think it's "pick your
>> poison".
>>
>> Alternatively, Ming's percpu_ref patch(*) may be worth a look.
>>
>> * https://www.spinics.net/lists/linux-block/msg56976.html1
> I'm not opposed to having this. Will require some more testing
> as this affects pretty much every driver out there..
>
> If we are going with a lightweight percpu_ref, can we just do
> it also for non-blocking hctx and have a single code-path?
> .
I tried to optimize the patch,support for non blocking queue and
blocking queue.
See next email.
next prev parent reply other threads:[~2020-08-07 9:04 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
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 [this message]
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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