Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [RESEND PATCH] sched: sd_llc_id initialized | Date | Wed, 15 Feb 2023 18:10:53 +0000 |
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On 14/02/23 17:54, Sun Shouxin wrote: > In my test,I use isolcpus to isolate cpu for specific, > and then I noticed different scenario when core binding. > > For example, the NUMA topology is as follows, > NUMA node0 CPU(s): 0-15,32-47 > NUMA node1 CPU(s): 16-31,48-63 > > and the 'isolcpus' is as follows, > isolcpus=14,15,30,31,46,47,62,63 > > One task initially running on the non-isolated core belong to NUMA0 > was bind to one isolated core on NUMA1, and then change its cpu affinity > to all cores, I notice the task can be scheduled back to the > non-isolated core on NUMA0. > > 1.taskset -pc 0-13 3512 (task running on core 1) > 2.taskset -pc 63 3512 (task running on isolated core 63) > 3.taskset -pc 0-63 3512 (task running on core 1) >
This is working as intended, no?
> Another case, one task initially running on the non-isolated core > belong to NUMA1 was bind to one isolated core on NUMA1, > and then change its cpu affinity to all cores, > the task can not be scheduled out and always run on the isolated core. > > 1.taskset -pc 16-29 3512 (task running on core 17) > 2.taskset -pc 63 3512 (task running on isolated core 63) > 3.taskset -pc 0-63 3512 (task still running on core 63 > and not schedule out) >
And this is also not wrong, since CPU63 is in the task's affinity mask.
That said, I can see that in this case we'd want the task to use other CPUs if it makes sense wrt load balance.
However, since CPU63 is attached to a NULL sched_domain, AFAIA your solution is at the mercy of the @prev and @target CPUs passed to select_idle_sibling(). So this might only work if the waker is on a non-isolated CPU.
I don't think your patch is wrong, but I don't think it entirely fixes the issue either. Unfortunately, due to isolated CPUs being attached to NULL sched_domains, there isn't a magic solution as the majority of scheduler decisions are based on these.
A safe bet would be to exclude isolated CPUs from the affinity of your non-critical tasks. Things like TuneD [1] and/or cpusets could help.
[1]: https://github.com/redhat-performance/tuned
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