From: Sagi Grimberg <sagi@grimberg.me>
To: Long Li <longli@microsoft.com>, Christoph Hellwig <hch@lst.de>,
Ming Lei <ming.lei@redhat.com>
Cc: Keith Busch <kbusch@kernel.org>, Jens Axboe <axboe@fb.com>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>
Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue
Date: Mon, 11 Nov 2019 17:35:57 -0800
Message-ID: <e03177f7-852c-d069-ddb0-4ab8a2cf5f56@grimberg.me> (raw)
In-Reply-To: <CY4PR21MB0741004E62F9C50B8EF7DA9ECE770@CY4PR21MB0741.namprd21.prod.outlook.com>
>> Subject: Re: [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-
>> mapping queue
>>
>> On Fri, Nov 08, 2019 at 11:55:08AM +0800, Ming Lei wrote:
>>> f9dde187fa92("nvme-pci: remove cq check after submission") removes cq
>>> check after submission, this change actually causes performance
>>> regression on some NVMe drive in which single nvmeq handles requests
>>> originated from more than one blk-mq sw queues(call it multi-mapping
>>> queue).
>>
>>> Follows test result done on Azure L80sv2 guest with NVMe drive(
>>> Microsoft Corporation Device b111). This guest has 80 CPUs and 10 numa
>>> nodes, and each NVMe drive supports 8 hw queues.
>>
>> Have you actually seen this on a real nvme drive as well?
>>
>> Note that it is kinda silly to limit queues like that in VMs, so I really don't think
>> we should optimize the driver for this particular case.
>
> I tested on an Azure L80s_v2 VM with newer Samsung P983 NVMe SSD (with 32 hardware queues). Tests also showed soft lockup when 32 queues are shared by 80 CPUs.
>
> The issue will likely show up if the number of NVMe hardware queues is less than the number of CPUs. I think this may be a likely configuration on a very large system. (e.g. the largest VM on Azure has 416 cores)
This makes sense. As long as there is a cpu core that keeps feeding the
sq nothing prevents from the irq handler to run forever...
_______________________________________________
Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme
next prev parent reply index
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-08 3:55 [PATCH 0/2] nvme-pci: improve IO performance via poll after batch submission Ming Lei
2019-11-08 3:55 ` [PATCH 1/2] nvme-pci: move sq/cq_poll lock initialization into nvme_init_queue Ming Lei
2019-11-08 4:12 ` Keith Busch
2019-11-08 7:09 ` Ming Lei
2019-11-08 3:55 ` [PATCH 2/2] nvme-pci: poll IO after batch submission for multi-mapping queue Ming Lei
2019-11-11 20:44 ` Christoph Hellwig
2019-11-12 0:33 ` Long Li
2019-11-12 1:35 ` Sagi Grimberg [this message]
2019-11-12 2:39 ` Ming Lei
2019-11-12 16:25 ` Hannes Reinecke
2019-11-12 16:49 ` Keith Busch
2019-11-12 17:29 ` Hannes Reinecke
2019-11-13 3:05 ` Ming Lei
2019-11-13 3:17 ` Keith Busch
2019-11-13 3:57 ` Ming Lei
2019-11-12 21:20 ` Long Li
2019-11-12 21:36 ` Keith Busch
2019-11-13 0:50 ` Long Li
2019-11-13 2:24 ` Ming Lei
2019-11-12 2:07 ` Ming Lei
2019-11-12 1:44 ` Sagi Grimberg
2019-11-12 9:56 ` Ming Lei
2019-11-12 17:35 ` Sagi Grimberg
2019-11-12 21:17 ` Long Li
2019-11-12 23:44 ` Jens Axboe
2019-11-13 2:47 ` Ming Lei
2019-11-12 18:11 ` Nadolski, Edmund
2019-11-13 13:46 ` Ming Lei
Reply instructions:
You may reply publically to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=e03177f7-852c-d069-ddb0-4ab8a2cf5f56@grimberg.me \
--to=sagi@grimberg.me \
--cc=axboe@fb.com \
--cc=hch@lst.de \
--cc=kbusch@kernel.org \
--cc=linux-nvme@lists.infradead.org \
--cc=longli@microsoft.com \
--cc=ming.lei@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Linux-NVME Archive on lore.kernel.org
Archives are clonable:
git clone --mirror https://lore.kernel.org/linux-nvme/0 linux-nvme/git/0.git
# If you have public-inbox 1.1+ installed, you may
# initialize and index your mirror using the following commands:
public-inbox-init -V2 linux-nvme linux-nvme/ https://lore.kernel.org/linux-nvme \
linux-nvme@lists.infradead.org
public-inbox-index linux-nvme
Example config snippet for mirrors
Newsgroup available over NNTP:
nntp://nntp.lore.kernel.org/org.infradead.lists.linux-nvme
AGPL code for this site: git clone https://public-inbox.org/public-inbox.git