On 06/05/2020 14:37, Juri Lelli wrote:
> On 06/05/20 12:54, Dietmar Eggemann wrote:
>> On 27/04/2020 10:37, Dietmar Eggemann wrote:
[...]
>> There is an issue w/ excl. cpusets and cpuset.sched_load_balance=0. The
>> latter is needed to demonstrate the problem since DL task affinity can't
>> be altered.
>>
>> A CPU in such a cpuset has its rq attached to def_root_domain which does
>> not have its 'sum_cpu_capacity' properly set.
>
> Hummm, but if sched_load_balance is disabled it means that we've now got
> a subset of CPUs which (from a DL AC pow) are partitioned. So, I'd tend
Yes, the CPUs of the cpuset w/ cpuset.sched_load_balance=0 (cpuset B in
the example).
> to say that we actually want to check new tasks bw requirement against
> the available bandwidth of the particular CPU they happen to be running
> (and will continue to run) when setscheduler is called.
By 'available bandwidth of the particular CPU' you refer to
'\Sum_{cpu_rq(i)->rd->span} CPU capacity', right?
This is what this fix tries to achieve. Regardless whether cpu_rq(i)->rd
is a 'real' rd or the def_root_domain, dl_bw_capacity() will now always
return '\Sum_{cpu_rq(i)->rd->span} CPU capacity'
> If then load balance is enabled again, AC check we did above should
> still be valid for all tasks admitted in the meantime, no?
Example (w/ this fix) on Juno [L b b L L L], capacity_orig_of(L)=446 :
mkdir /sys/fs/cgroup/cpuset/A
echo 0 > /sys/fs/cgroup/cpuset/A/cpuset.mems
echo 1 > /sys/fs/cgroup/cpuset/A/cpuset.cpu_exclusive
echo 0-2 > /sys/fs/cgroup/cpuset/A/cpuset.cpus
mkdir /sys/fs/cgroup/cpuset/B
echo 0 > /sys/fs/cgroup/cpuset/B/cpuset.mems
echo 1 > /sys/fs/cgroup/cpuset/B/cpuset.cpu_exclusive
echo 3-5 > /sys/fs/cgroup/cpuset/B/cpuset.cpus
echo 0 > /sys/fs/cgroup/cpuset/B/cpuset.sched_load_balance
echo 0 > /sys/fs/cgroup/cpuset/cpuset.sched_load_balance
echo $$ > /sys/fs/cgroup/cpuset/B/tasks
chrt -d --sched-runtime 8000 --sched-period 16000 -p 0 $$
...
[ 144.920102] __dl_bw_capacity CPU3 rd->span=3-5 return 1338
[ 144.925607] sched_dl_overflow: [bash 1999] task_cpu(p)=3 cap=1338
cpus_ptr=3-5
[ 144.932841] __dl_bw_capacity CPU3 rd->span=3-5 return 1338
...
echo 1 > /sys/fs/cgroup/cpuset/B/cpuset.sched_load_balance
echo $$ > /sys/fs/cgroup/cpuset/B/tasks
chrt -d --sched-runtime 8000 --sched-period 16000 -p 0 $$
...
[ 254.367982] __dl_bw_capacity CPU5 rd->span=3-5 return 1338
[ 254.373487] sched_dl_overflow: [bash 2052] task_cpu(p)=5 cap=1338
cpus_ptr=3-5
[ 254.380721] __dl_bw_capacity CPU5 rd->span=3-5 return 1338
...
Regardless of 'B/cpuset.sched_load_balance'
'\Sum_{cpu_rq(i)->rd->span} CPU capacity' stays 1338 (3*446)
So IMHO, DL AC check stays intact.
