Re: [PATCH 2/2] sched/core: Avoid unnecessary update in tg_set_cfs_bandwidth

[Chuyi Zhou]

在 2024/7/23 06:24, Benjamin Segall 写道:
> Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> writes:
>
> > In the kubernetes production environment, we have observed a high
> > frequency of writes to cpu.max, approximately every 2~4 seconds for each
> > cgroup, with the same value being written each time. This can result in
> > unnecessary overhead, especially on machines with a large number of CPUs
> > and cgroups.
> >
> > This is because kubelet and runc attempt to persist resource
> > configurations through frequent updates with same value in this manner.
> > While optimizations can be made to kubelet and runc to avoid such
> > overhead(e.g. check the current value of cpu request/limit before writing
> > to cpu.max), it is still worth to bail out from tg_set_cfs_bandwidth() if
> > we attempt to update with the same value.
>
> Yeah, this is silly of userspace, but we also do the same sort of check
> for shares, so sure.
>
> We do need it to be inside of a lock though, multiple threads could
> in theory write to the file at once. Just move it down inside of
> cfs_constraints_mutex and that's fine.

Thanks, I will send v2 later.