On Tue, Feb 06, 2024 at 01:56:23PM +0100, Frederic Weisbecker wrote: > Le Wed, Jan 17, 2024 at 12:15:07PM -0500, Waiman Long a écrit : > > > > On 1/17/24 12:07, Tejun Heo wrote: > > > Hello, > > > > > > On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote: > > > > The first 2 patches are adopted from Federic with minor twists to fix > > > > merge conflicts and compilation issue. The rests are for implementing > > > > the new cpuset.cpus.isolation_full interface which is essentially a flag > > > > to globally enable or disable full CPU isolation on isolated partitions. > > > I think the interface is a bit premature. The cpuset partition feature is > > > already pretty restrictive and makes it really clear that it's to isolate > > > the CPUs. I think it'd be better to just enable all the isolation features > > > by default. If there are valid use cases which can't be served without > > > disabling some isolation features, we can worry about adding the interface > > > at that point. > > > > My current thought is to make isolated partitions act like isolcpus=domain, > > additional CPU isolation capabilities are optional and can be turned on > > using isolation_full. However, I am fine with making all these turned on by > > default if it is the consensus. > > Right it was the consensus last time I tried. Along with the fact that mutating > this isolation_full set has to be done on offline CPUs to simplify the whole > picture. > > So lemme try to summarize what needs to be done: > > 1) An all-isolation feature file (that is, all the HK_TYPE_* things) on/off for > now. And if it ever proves needed, provide a way later for more finegrained > tuning. > > 2) This file must only apply to offline CPUs because it avoids migrations and > stuff. > > 3) I need to make RCU NOCB tunable only on offline CPUs, which isn't that much > changes. > > 4) HK_TYPE_TIMER: > * Wrt. timers in general, not much needs to be done, the CPUs are > offline. But: > * arch/x86/kvm/x86.c does something weird > * drivers/char/random.c might need some care > * watchdog needs to be (de-)activated > > 5) HK_TYPE_DOMAIN: > * This one I fear is not mutable, this is isolcpus... Except for HK_TYPE_DOMAIN, i have never seen anyone use any of this flags. > > 6) HK_TYPE_MANAGED_IRQ: > * I prefer not to think about it :-) > > 7) HK_TYPE_TICK: > * Maybe some tiny ticks internals to revisit, I'll check that. > * There is a remote tick to take into consideration, but again the > CPUs are offline so it shouldn't be too complicated. > > 8) HK_TYPE_WQ: > * Fortunately we already have all the mutable interface in place. > But we must make it live nicely with the sysfs workqueue affinity > files. > > 9) HK_FLAG_SCHED: > * Oops, this one is ignored by nohz_full/isolcpus, isn't it? > Should be removed? > > 10) HK_TYPE_RCU: > * That's point 3) and also some kthreads to affine, which leads us > to the following in HK_TYPE_KTHREAD: > > 11) HK_FLAG_KTHREAD: > * I'm guessing it's fine as long as isolation_full is also an > isolated partition. Then unbound kthreads shouldn't run there. > > 12) HK_TYPE_MISC: > * Should be fine as ILB isn't running on offline CPUs. > > Thanks. > >
