On 11/20/20 7:20 PM, Christopher Lameter wrote:
On Tue, 17 Nov 2020, Marcelo Tosatti wrote:
> So what we would need would be something like a sysctl that puts the
> system into a quiet state by completing all workqueue items. Idle all
> subsystems that need it and put the cpu into NOHZ mode.
Are you suggesting that instead of a specific file to control vmstat
workqueue only, a more generic sysctl could be used?
Yes. Introduce a sysctl to quiet down the system. Clean caches that will
trigger kernel threads and whatever else is pending on that processor.
Please CC linux-api on future postings that introduce stuff like this.
About NOHZ mode: the CPU should enter NOHZ automatically as soon as
there is a single thread running, so unclear why that would be needed.
There are typically pending actions that still trigger interruptions.
If you would immediately quiet down the system if there is only one thread
runnable then you would compromise system performance through frequent
counter folding and cache cleaning etc.
If someone goes through the trouble of setting up NOHZ, these
disruptions should be only temporary and happen during the setup, no?
