Re: [PATCH v7 09/10] blk-mq: prevent offlining hk CPUs with associated online isolated CPUs

[Ming Lei]

On Wed, Jul 02, 2025 at 06:33:59PM +0200, Daniel Wagner wrote:
> When isolcpus=io_queue is enabled, and the last housekeeping CPU for a
> given hctx goes offline, there would be no CPU left to handle I/O. To
> prevent I/O stalls, prevent offlining housekeeping CPUs that are still
> serving isolated CPUs.
> 
> When isolcpus=io_queue is enabled and the last housekeeping CPU
> for a given hctx goes offline, no CPU would be left to handle I/O.
> To prevent I/O stalls, disallow offlining housekeeping CPUs that are
> still serving isolated CPUs.

If you do so, cpu offline is failed, and this change is user visible, please
document the cpu offline failure limit on Documentation/admin-guide/kernel-parameters.txt.
in the next patch.

Thanks,
Ming