linux-kernel - Question about nohz and sysidle

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Message-ID: <b881759b-d281-fdc3-71b7-4429d84cd734@huawei.com>
Date:   Mon, 14 Feb 2022 16:28:20 +0800
From:   Yu Liao <liaoyu15@...wei.com>
To:     <fweisbec@...il.com>, <paulmck@...ux.vnet.ibm.com>
CC:     <linux-kernel@...r.kernel.org>, <liwei391@...wei.com>
Subject: Question about nohz and sysidle

Hi,

I'm working on an issue about nohz. When NO_HZ_FULL is enabled, CPU 0 
handles the timekeeping duty on behalf of all other CPUs, which means 
CPU 0 never stop tick even in sysidle state. This is a powersaving issue.

I found Frederic's patchset (nohz: Support sysidle) in the below link.
https://lore.kernel.org/all/1406569056-30217-1-git-send-email-fweisbec@gmail.com/
But these patches haven't been merged into mainline yet and sysidle 
state detection has been removed by commit fe5ac724d81a (rcu: Remove 
nohz_full full-system-idle state machine) as well.

I tried Frederic's patches and it does work, why are we no longer 
working on stopping timekeeping duty when all full dynticks CPUs are idle?

Thanks,

Yu