On 21/10/2024 11:31, Ming Lei wrote:
On Mon, Oct 21, 2024 at 10:05:34AM +0300, Sagi Grimberg wrote:
On 21/10/2024 4:39, Ming Lei wrote:
On Sun, Oct 20, 2024 at 10:40:41PM +0800, zhuxiaohui wrote:
From: Zhu Xiaohui <zhuxiaohui.400@xxxxxxxxxxxxx>
It is observed that nvme connect to a nvme over fabric target will
always fail when 'nohz_full' is set.
In commit a46c27026da1 ("blk-mq: don't schedule block kworker on
isolated CPUs"), it clears hctx->cpumask for all isolate CPUs,
and when nvme connect to a remote target, it may fails on this stack:
blk_mq_alloc_request_hctx+1
__nvme_submit_sync_cmd+106
nvmf_connect_io_queue+181
nvme_tcp_start_queue+293
nvme_tcp_setup_ctrl+948
nvme_tcp_create_ctrl+735
nvmf_dev_write+532
vfs_write+237
ksys_write+107
do_syscall_64+128
entry_SYSCALL_64_after_hwframe+118
due to that the given blk_mq_hw_ctx->cpumask is cleared with no available
blk_mq_ctx on the hw queue.
This patch introduce a new blk_mq_req_flags_t flag 'BLK_MQ_REQ_ARB_MQ'
as well as a nvme_submit_flags_t 'NVME_SUBMIT_ARB_MQ' which are used to
indicate that block layer can fallback to a blk_mq_ctx whose cpu
is not isolated.
blk_mq_alloc_request_hctx()
...
cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
...
It can happen in case of non-cpu-isolation too, such as when this hctx hasn't
online CPUs, both are same actually from this viewpoint.
It is one long-time problem for nvme fc.
For what nvmf is using blk_mq_alloc_request_hctx() is not important. It just
needs a tag from that hctx. the request execution is running where
blk_mq_alloc_request_hctx() is running.
I am afraid that just one tag from the specified hw queue isn't enough.
The connection request needs to be issued to the hw queue & completed.
Without any online CPU for this hw queue, the request can't be completed
in case of managed-irq.
None of the consumers of this API use managed-irqs. the networking stack
takes care of steering irq vectors to online cpus.
