On Tue, Jul 27, 2021 at 11:56:25AM -0400, Waiman Long wrote: > On 7/27/21 7:42 AM, Frederic Weisbecker wrote: > > On Tue, Jul 20, 2021 at 10:18:31AM -0400, Waiman Long wrote: > > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=TBD > > > > > > commit 994fb794cb252edd124a46ca0994e37a4726a100 > > > Author: Waiman Long <longman@xxxxxxxxxx> > > > Date: Sat, 19 Jun 2021 13:28:19 -0400 > > > > > > cgroup/cpuset: Add a new isolated cpus.partition type > > > > > > Cpuset v1 uses the sched_load_balance control file to determine if load > > > balancing should be enabled. Cpuset v2 gets rid of sched_load_balance > > > as its use may require disabling load balancing at cgroup root. > > > > > > For workloads that require very low latency like DPDK, the latency > > > jitters caused by periodic load balancing may exceed the desired > > > latency limit. > > > > > > When cpuset v2 is in use, the only way to avoid this latency cost is to > > > use the "isolcpus=" kernel boot option to isolate a set of CPUs. After > > > the kernel boot, however, there is no way to add or remove CPUs from > > > this isolated set. For workloads that are more dynamic in nature, that > > > means users have to provision enough CPUs for the worst case situation > > > resulting in excess idle CPUs. > > > > > > To address this issue for cpuset v2, a new cpuset.cpus.partition type > > > "isolated" is added which allows the creation of a cpuset partition > > > without load balancing. This will allow system administrators to > > > dynamically adjust the size of isolated partition to the current need > > > of the workload without rebooting the system. > > > > > > Signed-off-by: Waiman Long <longman@xxxxxxxxxx> > > > > > > Signed-off-by: Waiman Long <longman@xxxxxxxxxx> > > Nice! And while we are adding a new ABI, can we take advantage of that and > > add a specific semantic that if a new isolated partition matches a subset of > > "isolcpus=", it automatically maps to it. This means that any further > > modification to that isolated partition will also modify the associated > > isolcpus= subset. > > > > Or to summarize, when we create a new isolated partition, remove the associated > > CPUs from isolcpus= ? > > We can certainly do that as a follow-on. I'm just concerned that this feature gets merged before we add that new isolcpus= implicit mapping, which technically is a new ABI. Well I guess I should hurry up and try to propose a patchset quickly once I'm back from vacation :-) > Another idea that I have been > thinking about is to automatically generating a isolated partition under > root to match the given isolcpus parameter when the v2 filesystem is > mounted. That needs more experimentation and testing to verify that it can > work. I thought about that too, mounting an "isolcpus" subdirectory withing the top cpuset but I was worried it could break userspace that wouldn't expect that new thing to show up. Thanks.
