Messages in this thread | | | Date | Mon, 18 Sep 2023 09:47:02 -0400 | Subject | Re: [PATCH 1/1] cgroup/cpuset: Rebuild sched domains if isolated partition changed | From | Waiman Long <> |
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On 9/18/23 03:07, Pierre Gondois wrote: > Hello Longman, > > On 9/17/23 18:51, Waiman Long wrote: >> On 9/15/23 11:45, Pierre Gondois wrote: >>> When an isolated parition is created, the sched domains (sds) are >>> rebuilt and the sds of the isolated CPUs are detached. This only >>> happens at the creation of the isolated parition. Updating >>> the cpuset of the partition doesn't rebuild the sds: >>> >>> To reproduce: >>> # ls /sys/kernel/debug/sched/domains/cpu0/ >>> domain0 >>> # ls /sys/kernel/debug/sched/domains/cpu1/ >>> domain0 >>> # >>> # mkdir cgroup >>> # mount -t cgroup2 none cgroup/ >>> # mkdir cgroup/A1/ >>> # echo "+cpuset" > cgroup/cgroup.subtree_control >>> # echo 0-3 > cgroup/A1/cpuset.cpus >>> # echo isolated > cgroup/A1/cpuset.cpus.partition >>> # >>> # ls /sys/kernel/debug/sched/domains/cpu0/ >>> # ls /sys/kernel/debug/sched/domains/cpu1/ >>> # >>> # echo 0 > cgroup/A1/cpuset.cpus >>> # ls /sys/kernel/debug/sched/domains/cpu0/ >>> # ls /sys/kernel/debug/sched/domains/cpu1/ >>> # >>> >>> Here CPU1 should have a sched domain re-attached. >>> >>> Signed-off-by: Pierre Gondois <pierre.gondois@arm.com> >>> --- >>> kernel/cgroup/cpuset.c | 12 ++++++++---- >>> 1 file changed, 8 insertions(+), 4 deletions(-) >>> >>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c >>> index 58e6f18f01c1..e3eb27ff9b68 100644 >>> --- a/kernel/cgroup/cpuset.c >>> +++ b/kernel/cgroup/cpuset.c >>> @@ -1680,11 +1680,15 @@ static void update_cpumasks_hier(struct >>> cpuset *cs, struct tmpmasks *tmp, >>> * empty cpuset is changed, we need to rebuild sched >>> domains. >>> * On default hierarchy, the cpuset needs to be a partition >>> * root as well. >>> + * Also rebuild sched domains if the cpuset of an isolated >>> + * partition changed. >>> */ >>> - if (!cpumask_empty(cp->cpus_allowed) && >>> - is_sched_load_balance(cp) && >>> - (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) || >>> - is_partition_valid(cp))) >>> + if ((!cpumask_empty(cp->cpus_allowed) && >>> + is_sched_load_balance(cp) && >>> + (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) || >>> + is_partition_valid(cp))) || >>> + (cp->partition_root_state == PRS_ISOLATED || >>> + cp->partition_root_state == PRS_INVALID_ISOLATED)) >>> need_rebuild_sched_domains = true; >>> rcu_read_lock(); >> >> Thanks for spotting the problem and sending out a patch to fix it. >> However, it should be done in the update_cpumask(). The sched_domain >> rebuild in update_cpumasks_hier() is supposed to be used for impacted >> descendant cpusets lower down in the hierarchy. >> >> Anyway, I believe this problem should have been fixed in commit >> a86ce68078b2 ("cgroup/cpuset: Extract out CS_CPU_EXCLUSIVE & >> CS_SCHED_LOAD_BALANCE handling") recently merged into the v6.6 kernel. >> Would you mind testing the latest upstream kernel to see if this problem >> is gone or not? > > Yes right, v6.6-rc2 kernel doesn't have this issue. My bad for not > updating > it ... > > However I think the second issue described in the cover letter can > still be > reproduced on v6.6-rc2. This present patch was not aiming to fix it > though. > > Commands: > # mkdir cgroup > # mount -t cgroup2 none cgroup/ > # mkdir cgroup/A1 cgroup/B1 > # echo "+cpuset" > cgroup/cgroup.subtree_control > # echo 0-3 > cgroup/A1/cpuset.cpus > # echo isolated > cgroup/A1/cpuset.cpus.partition > # echo 4-6 > cgroup/B1/cpuset.cpus > # cat cgroup/A1/cpuset.cpus.partition > isolated > # echo 0-4 > cgroup/A1/cpuset.cpus > # cat cgroup/A1/cpuset.cpus.partition > isolated invalid (Cpu list in cpuset.cpus not exclusive) > # echo 0-3 > cgroup/A1/cpuset.cpus > # cat cgroup/A1/cpuset.cpus.partition > isolated invalid (Cpu list in cpuset.cpus not exclusive) > > Cgroup A1 should be a valid isolated partition once its CPUs become > exclusive again I believe,
Yes, the current code doesn't always detect that an invalid partition can be valid again and turn it back on. Will try to fix that. In the mean time, a workaround is to do
# echo member > cgroup/A1/cpuset.cpus.partition # echo isolated > cgroup/A1/cpuset.cpus.partition
Thanks, Longman
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