From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-nvme@lists.infradead.org, Keith Busch <kbusch@kernel.org>,
Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>
Subject: Re: [PATCH] nvmet-rdma: Avoid o(n^2) loop in delete_ctrl
Date: Mon, 6 May 2024 10:36:11 +0300 [thread overview]
Message-ID: <c7fb5eeb-1dc7-4cf1-875b-b941447b7be0@grimberg.me> (raw)
In-Reply-To: <20240506055020.GA5059@lst.de>
On 06/05/2024 8:50, Christoph Hellwig wrote:
> On Sun, May 05, 2024 at 01:39:44PM +0300, Sagi Grimberg wrote:
>> From: Sagi Grimberg <sagi.grimberg@vastdata.com>
>>
>> When deleting a nvmet-rdma ctrl, we essentially loop over all
>> queues that belong to the controller and schedule a removal of
>> each. Instead of restarting the loop every time a queue is found,
>> do a simple safe list traversal.
>>
>> This addresses an unneeded time spent scheduling queue removal in
>> cases there a lot of queues.
> I think the original reason for this was to avoid lock order dependencies
> and/or deadlocks, I wish I would have documented that better. Looking at
> the current version __nvmet_rdma_queue_disconnect I can't find any
> obvious problem, but rdma_disconnect is a bit of a block box from
> the driver POV.
Yes rdma_disconnect is a black box (essentially move the qp to err state
and send
a cm disconnect request/response). But it is not dependent on
nvmet_rdma_queue_mutex. It is true that in the cm handler we may take this
lock, but that handler has its own context.
The same pattern is used in nvmet_rdma_destroy_port_queues() and
nvmet_rdma_remove_one()
> Did you test this extensively with lockdep enabled?
I can't say this is extensively tested. I can run blktests and make sure
lockdep
is enabled.
>
>> + list_for_each_entry_safe(queue, tmp, &nvmet_rdma_queue_list, queue_list) {
> Nit: overly long line here. Maybe just rename tmp to n?
Sure.
prev parent reply other threads:[~2024-05-06 7:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-05 10:39 [PATCH] nvmet-rdma: Avoid o(n^2) loop in delete_ctrl Sagi Grimberg
2024-05-06 5:50 ` Christoph Hellwig
2024-05-06 7:36 ` Sagi Grimberg [this message]
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