On 7/1/24 09:21, Ming Lei wrote:
On Mon, Jul 01, 2024 at 09:08:32AM +0200, Daniel Wagner wrote:
On Sun, Jun 30, 2024 at 09:39:59PM GMT, Ming Lei wrote:
Make group_cpus_evenly aware of isolcpus configuration and use the
housekeeping CPU mask as base for distributing the available CPUs into
groups.
Fixes: 11ea68f553e2 ("genirq, sched/isolation: Isolate from handling managed interrupts")
isolated CPUs are actually handled when figuring out irq effective mask,
so not sure how commit 11ea68f553e2 is wrong, and what is fixed in this
patch from user viewpoint?
IO queues are allocated/spread on the isolated CPUs and if there is an
thread submitting IOs from an isolated CPU it will cause noise on the
isolated CPUs. The question is this a use case you need/want to support?
I have talked RH Openshift team weeks ago and they have such usage.
userspace is free to run any application from isolated CPUs via 'taskset
-c' even though 'isolcpus=' is passed from command line.
Kernel can not add such new constraint on userspace.
We have customers who are complaining that even with isolcpus provided
they still see IO noise on the isolated CPUs.
That is another issue, which has been fixed by the following patch:
a46c27026da1 blk-mq: don't schedule block kworker on isolated CPUs
Hmm. Just when I thought I understood the issue ...
How is this supposed to work, then, given that I/O can be initiated
from the isolated CPUs?
I would have accepted that we have two scheduling domains, blk-mq is
spread across all cpus, and the blk-mq cpusets are arranged according
to the isolcpu settings.
Then we can initiate I/O from the isolated cpus, and the scheduler
would 'magically' ensure that everything is only run on isolated cpus.
But that patch would completely counteract such a setup, as during
I/O we more often than not will invoke kblockd, which then would cause
cross-talk on non-isolated cpus.
What is the idea here?
Confused,
Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@xxxxxxx +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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