| Message ID | 20240117163511.88173-1-longman@redhat.com |
|---|---|
| Headers | show |
| Series | cgroup/cpuset: Support RCU_NOCB on isolated partitions | expand |
On 2/6/24 07:56, 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. That is more or less the current plan. As detailed below, HK_TYPE_DOMAIN & HK_TYPE_WQ isolation are included in the isolated partitions by default. I am also thinking about including other relatively cheap isolation flags by default. The expensive ones will have to be enabled via isolation_full. > > 2) This file must only apply to offline CPUs because it avoids migrations and > stuff. Well, the process of first moving the CPUs offline first is rather expensive. I won't mind doing some partial offlining based on the existing set of teardown and bringup callbacks, but I would try to avoid fully offlining the CPUs first. > > 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... HK_TYPE_DOMAIN is already available via the current cpuset isolated partition functionality. What I am currently doing is to extend that to other HK_TYPE* 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. HK_TYPE_WQ is basically done and it is going to work properly with the workqueue affinity sysfs files. From the workqueue of view, HK_TYPE_WQ is currently treated the same as HK_TYPE_DOMAIN. > > 9) HK_FLAG_SCHED: > * Oops, this one is ignored by nohz_full/isolcpus, isn't it? > Should be removed? I don't think HK_FLAG_SCHED is being used at all. So I believe we should remove it to avoid confusion. > > 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. Yes, isolation_full applies only to isolated partitions. It extends the amount of CPU isolation by enabling all the other CPU available isolation flags. Cheers, Longman
On 1/19/24 05:24, Paul E. McKenney wrote: > On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote: >> This patch series is based on the RFC patch from Frederic [1]. Instead >> of offering RCU_NOCB as a separate option, it is now lumped into a >> root-only cpuset.cpus.isolation_full flag that will enable all the >> additional CPU isolation capabilities available for isolated partitions >> if set. RCU_NOCB is just the first one to this party. Additional dynamic >> CPU isolation capabilities will be added in the future. >> >> 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. >> On read, it also shows the CPU isolation capabilities that are currently >> enabled. RCU_NOCB requires that the rcu_nocbs option be present in >> the kernel boot command line. Without that, the rcu_nocb functionality >> cannot be enabled even if the isolation_full flag is set. So we allow >> users to check the isolation_full file to verify that if the desired >> CPU isolation capability is enabled or not. >> >> Only sanity checking has been done so far. More testing, especially on >> the RCU side, will be needed. > There has been some discussion of simplifying the (de-)offloading code > to handle only offline CPUs. Along with some discussion of eliminating > the (de-)offloading capability altogehter. > > We clearly should converge on the capability to be provided before > exposing this to userspace. ;-) Would you mind giving me a pointer to the discussion of simplifying the de-offloading code to handle only offline CPUs? Thanks, Longman
This patch series is based on the RFC patch from Frederic [1]. Instead of offering RCU_NOCB as a separate option, it is now lumped into a root-only cpuset.cpus.isolation_full flag that will enable all the additional CPU isolation capabilities available for isolated partitions if set. RCU_NOCB is just the first one to this party. Additional dynamic CPU isolation capabilities will be added in the future. 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. On read, it also shows the CPU isolation capabilities that are currently enabled. RCU_NOCB requires that the rcu_nocbs option be present in the kernel boot command line. Without that, the rcu_nocb functionality cannot be enabled even if the isolation_full flag is set. So we allow users to check the isolation_full file to verify that if the desired CPU isolation capability is enabled or not. Only sanity checking has been done so far. More testing, especially on the RCU side, will be needed. [1] https://lore.kernel.org/lkml/20220525221055.1152307-1-frederic@kernel.org/ Frederic Weisbecker (2): rcu/nocb: Pass a cpumask instead of a single CPU to offload/deoffload rcu/nocb: Prepare to change nocb cpumask from CPU-hotplug protected cpuset caller Waiman Long (6): rcu/no_cb: Add rcu_nocb_enabled() to expose the rcu_nocb state cgroup/cpuset: Better tracking of addition/deletion of isolated CPUs cgroup/cpuset: Add cpuset.cpus.isolation_full cgroup/cpuset: Enable dynamic rcu_nocb mode on isolated CPUs cgroup/cpuset: Document the new cpuset.cpus.isolation_full control file cgroup/cpuset: Update test_cpuset_prs.sh to handle cpuset.cpus.isolation_full Documentation/admin-guide/cgroup-v2.rst | 24 ++ include/linux/rcupdate.h | 15 +- kernel/cgroup/cpuset.c | 237 ++++++++++++++---- kernel/rcu/rcutorture.c | 6 +- kernel/rcu/tree_nocb.h | 118 ++++++--- .../selftests/cgroup/test_cpuset_prs.sh | 23 +- 6 files changed, 337 insertions(+), 86 deletions(-)