Messages in this thread |  | | From | Waiman Long <> | Subject | Re: [PATCH v3 6/9] cgroup/cpuset: Add a new isolated cpus.partition type | Date | Tue, 27 Jul 2021 11:56:25 -0400 |
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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@redhat.com> >> 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@redhat.com> >> >> Signed-off-by: Waiman Long <longman@redhat.com> > 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. 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.
Cheers, Longman
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