Re: [PATCH V3] blk-mq: don't schedule block kworker on isolated CPUs

[Ming Lei <ming.lei@redhat.com>]

On Wed, Oct 25, 2023 at 10:57:37AM +0800, Ming Lei wrote:
> Kernel parameter of `isolcpus=` or 'nohz_full=' are used for isolating CPUs
> for specific task, and user often won't want block IO to disturb these CPUs,
> also long IO latency may be caused if blk-mq kworker is scheduled on these
> isolated CPUs.
> 
> Kernel workqueue only respects this limit for WQ_UNBOUND, for bound wq,
> the responsibility should be on wq user.
> 
> So don't not run block kworker on isolated CPUs by ruling out isolated CPUs
> from hctx->cpumask. Meantime in cpuhp handler, use queue map to check if
> all CPUs in this hw queue are offline, this way can avoid any cost in fast
> IO code path.
> 
> Cc: Juri Lelli <juri.lelli@redhat.com>
> Cc: Andrew Theurer <atheurer@redhat.com>
> Cc: Joe Mario <jmario@redhat.com>
> Cc: Sebastian Jug <sejug@redhat.com>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Bart Van Assche <bvanassche@acm.org>
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
> 
> V3:
> 	- avoid to check invalid cpu as reported by Bart
> 	- take current cpu(to be offline, not done yet) into account
> 	- simplify blk_mq_hctx_has_online_cpu()

Hello Jens and Guys,

Ping...

thanks,
Ming