From: Hannes Reinecke <hare@suse.de>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, linux-nvme@lists.infradead.org,
Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>, Daniel Wagner <dwagner@suse.de>,
Wen Xiong <wenxiong@us.ibm.com>,
John Garry <john.garry@huawei.com>
Subject: Re: [PATCH 0/2] blk-mq: fix blk_mq_alloc_request_hctx
Date: Wed, 30 Jun 2021 10:18:37 +0200 [thread overview]
Message-ID: <5f304121-38ce-034b-2d17-93d136c77fe6@suse.de> (raw)
In-Reply-To: <20210629074951.1981284-1-ming.lei@redhat.com>
On 6/29/21 9:49 AM, Ming Lei wrote:
> Hi,
>
> blk_mq_alloc_request_hctx() is used by NVMe fc/rdma/tcp/loop to connect
> io queue. Also the sw ctx is chosen as the 1st online cpu in hctx->cpumask.
> However, all cpus in hctx->cpumask may be offline.
>
> This usage model isn't well supported by blk-mq which supposes allocator is
> always done on one online CPU in hctx->cpumask. This assumption is
> related with managed irq, which also requires blk-mq to drain inflight
> request in this hctx when the last cpu in hctx->cpumask is going to
> offline.
>
> However, NVMe fc/rdma/tcp/loop don't use managed irq, so we should allow
> them to ask for request allocation when the specified hctx is inactive
> (all cpus in hctx->cpumask are offline).
>
> Fix blk_mq_alloc_request_hctx() by adding/passing flag of
> BLK_MQ_F_NOT_USE_MANAGED_IRQ.
>
>
> Ming Lei (2):
> blk-mq: not deactivate hctx if the device doesn't use managed irq
> nvme: pass BLK_MQ_F_NOT_USE_MANAGED_IRQ for fc/rdma/tcp/loop
>
> block/blk-mq.c | 6 +++++-
> drivers/nvme/host/fc.c | 3 ++-
> drivers/nvme/host/rdma.c | 3 ++-
> drivers/nvme/host/tcp.c | 3 ++-
> drivers/nvme/target/loop.c | 3 ++-
> include/linux/blk-mq.h | 1 +
> 6 files changed, 14 insertions(+), 5 deletions(-)
>
> Cc: Sagi Grimberg <sagi@grimberg.me>
> Cc: Daniel Wagner <dwagner@suse. thede>
> Cc: Wen Xiong <wenxiong@us.ibm.com>
> Cc: John Garry <john.garry@huawei.com>
>
>
I have my misgivings about this patchset.
To my understanding, only CPUs present in the hctx cpumask are eligible
to submit I/O to that hctx.
Consequently if all cpus in that mask are offline, where is the point of
even transmitting a 'connect' request?
Shouldn't we rather modify the tagset to only refer to the current
online CPUs _only_, thereby never submit a connect request for hctx with
only offline CPUs?
Cheers,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer
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next prev parent reply other threads:[~2021-06-30 8:18 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-29 7:49 [PATCH 0/2] blk-mq: fix blk_mq_alloc_request_hctx Ming Lei
2021-06-29 7:49 ` [PATCH 1/2] blk-mq: not deactivate hctx if the device doesn't use managed irq Ming Lei
2021-06-29 12:39 ` Hannes Reinecke
2021-06-29 14:17 ` Ming Lei
2021-06-29 15:49 ` John Garry
2021-06-30 0:32 ` Ming Lei
2021-06-30 9:25 ` John Garry
2021-07-01 9:52 ` Christoph Hellwig
2021-06-29 23:30 ` Damien Le Moal
2021-06-30 18:58 ` Sagi Grimberg
2021-06-30 21:57 ` Damien Le Moal
2021-07-01 14:20 ` Keith Busch
2021-06-29 7:49 ` [PATCH 2/2] nvme: pass BLK_MQ_F_NOT_USE_MANAGED_IRQ for fc/rdma/tcp/loop Ming Lei
2021-06-30 8:15 ` Hannes Reinecke
2021-06-30 8:47 ` Ming Lei
2021-06-30 8:18 ` Hannes Reinecke [this message]
2021-06-30 8:42 ` [PATCH 0/2] blk-mq: fix blk_mq_alloc_request_hctx Ming Lei
2021-06-30 9:43 ` Hannes Reinecke
2021-06-30 9:53 ` Ming Lei
2021-06-30 18:59 ` Sagi Grimberg
2021-06-30 19:46 ` Hannes Reinecke
2021-06-30 23:59 ` Ming Lei
2021-07-01 8:00 ` Hannes Reinecke
2021-07-01 9:13 ` Ming Lei
2021-07-02 9:47 ` Daniel Wagner
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