Re: [PATCH v2 0/2] nvme-pci: add adaptive interrupt polling

[changfengnan]

More test data is available here.
https://docs.google.com/spreadsheets/d/1rer4Nl5HHxSO-D3NrrHuHSfpR9s1kLhpLjzh7h7Mbmw/edit?gid=875909538#gid=875909538

We’ve added tests for some NVMe drives with very poor performance, 
such as the HFS480GEJ8X176N (4k random write: 40k IOPS, 4k random
read: 700k IOPS) and the MZVL2480HBJD (4k random write: 20k IOPS,
4k random read: 130k IOPS).
We’ve also tested  performance on QLC.
There were a total of 3,280 test cases covering 13 different drive models.
Among these, 327 cases showed a steady improvement, with a maximum
improvement of 240% and a median of 29%. 
Meanwhile, 15 cases showed a regression, with a maximum regression of
-11% and a median of -7.4%.
Almost none of the regressions can be reliably reproduced, but that
doesn’t mean they didn’t occur—when we ran the tests again, similar
regressions appeared in about 10 different cases.

Here is more data compare to GSIM:
https://docs.google.com/spreadsheets/d/14-_lLyPO_Uxm0ou7K-AcQ9qPCuWUZK0-n5JTgqvgZJc/edit?gid=875909538#gid=875909538


> From: "Fengnan Chang"<changfengnan@xxxxxxxxxxxxx>
> Date:  Wed, Aug 26, 2026, 14:16
> Subject:  [PATCH v2 0/2] nvme-pci: add adaptive interrupt polling
> To: "Keith Busch"<kbusch@xxxxxxxxxx>, "Jens Axboe"<axboe@xxxxxxxxx>, "Christoph Hellwig"<hch@xxxxxx>, "Sagi Grimberg"<sagi@xxxxxxxxxxx>, <linux-nvme@xxxxxxxxxxxxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>, <jun1.zeng@xxxxxxxxx>, <anuj1072538@xxxxxxxxx>
> Cc: <guzebing@xxxxxxxxxxxxx>, "Fengnan Chang"<changfengnan@xxxxxxxxxxxxx>
> At high IOPS, interrupt handling can limit throughput, especially when
> multiple drives contend for CPU time.
> 
> Add an opt-in adaptive policy for I/O queues that use a dedicated MSI-X
> vector and do not use threaded interrupts. Each queue independently
> switches between interrupt and poll mode based on its recent completion
> rate.
> 
> In interrupt mode, wait for at least 8192 completions. If they arrive
> no more than 10 us apart on average, try polling. While polling, an
> hrtimer runs irq_poll to drain the completion queue. Before a window
> is full, polling may fall 20 us behind the interrupt-mode pace. After
> 8192 completions, polling must be strictly faster than interrupt mode.
> 
> If a try fails, go back to interrupt mode and measure again. After
> three failures in a row, stay in interrupt mode for 64 windows of
> completions before measuring again. If polling works, keep it for at
> most 64 windows, then go back to interrupt mode and measure again.
> 
> The module parameter is off by default and only sets the initial
> mode for new controllers. A per-controller sysfs file can change
> the mode later. The change freezes the namespace queues and waits
> for in-flight I/O to finish. Queues that use threaded, MSI, or
> legacy interrupts keep the regular interrupt handler.
> 
> Measured with 4 KiB random reads on Solidigm SB5PH27X076T, adaptive
> polling on versus off:
>                                      QD32      QD64      QD128
> one device, one job                 -0.08%    +31.56%   +30.95%
> fifteen devices, eight jobs/device  +188.03%  +236.46%  +231.38%
> 
> The fifteen-device aggregate with eight jobs per device increases
> from 13.48M / 13.47M / 13.47M IOPS to 38.83M / 45.31M / 44.64M IOPS.
> 
> Changes since v1:
> - Split the nvme_poll_cq() return-count change into a separate prep patch
>   (patch 1/2) so the functional change stands on its own.
> - Factor out nvme_irq_complete_batch() so the regular and adaptive
>   interrupt handlers share one batch-completion path.
> - Only call irq_poll_complete() when completions < budget, matching the
>   irq_poll contract; the previous boundary case could return the poll
>   object to the softirq list after it was already removed.
> - Clarify comments: document the NVMEQ_ADAPTIVE_* flags and the
>   dual-purpose retry_completions field, and reword the constant rationale.
> - Minor style/indentation fixes per review.
> 
> 
> Fengnan Chang (2):
>   nvme-pci: return completion count from nvme_poll_cq
>   nvme-pci: add adaptive interrupt polling
> 
>  Documentation/ABI/testing/sysfs-nvme |  17 +
>  drivers/nvme/host/Kconfig            |   1 +
>  drivers/nvme/host/pci.c              | 542 +++++++++++++++++++++++++--
>  3 files changed, 536 insertions(+), 24 deletions(-)
> 
> -- 
> 2.39.5 (Apple Git-154)
>