On Thu, Mar 14, 2024 at 12:46:54PM +0100, Tobias Huschle wrote: > On Tue, Mar 12, 2024 at 09:45:57AM +0000, Luis Machado wrote: > > On 3/11/24 17:05, Michael S. Tsirkin wrote: > > > > > > Are we going anywhere with this btw? > > > > > > > > > > I think Tobias had a couple other threads related to this, with other potential fixes: > > > > https://lore.kernel.org/lkml/20240228161018.14253-1-huschle@xxxxxxxxxxxxx/ > > > > https://lore.kernel.org/lkml/20240228161023.14310-1-huschle@xxxxxxxxxxxxx/ > > > > Sorry, Michael, should have provided those threads here as well. > > The more I look into this issue, the more things to ponder upon I find. > It seems like this issue can (maybe) be fixed on the scheduler side after all. > > The root cause of this regression remains that the mentioned kworker gets > a negative lag value and is therefore not elligible to run on wake up. > This negative lag is potentially assigned incorrectly. But I'm not sure yet. > > Anytime I find something that can address the symptom, there is a potential > root cause on another level, and I would like to avoid to just address a > symptom to fix the issue, wheras it would be better to find the actual > root cause. > > I would nevertheless still argue, that vhost relies rather heavily on the fact > that the kworker gets scheduled on wake up everytime. But I don't have a > proposal at hand that accounts for potential side effects if opting for > explicitly initiating a schedule. > Maybe the assumption, that said kworker should always be selected on wake > up is valid. In that case the explicit schedule would merely be a safety > net. > > I will let you know if something comes up on the scheduler side. There are > some more ideas on my side how this could be approached. Thanks a lot! To clarify it is not that I am opposed to changing vhost. I would like however for some documentation to exist saying that if you do abc then call API xyz. Then I hope we can feel a bit safer that future scheduler changes will not break vhost (though as usual, nothing is for sure). Right now we are going by the documentation and that says cond_resched so we do that. -- MST
