Re: status of BPF in conjunction with PREEMPT_RT for the 6.6 kernel?

[Hou Tao <houtao1@huawei.com>]

Hi,

On 1/10/2025 6:21 AM, Chris Friesen wrote:
> Hi,
>
> Back in 2019 there were some concerns raised
> (https://lwn.net/ml/bpf/20191017090500.ienqyium2phkxpdo@linutronix.de/#t)
> around using BPF in conjunction with PREEMPT_RT.
>
> In the context of the 6.6 kernel and the corresponding PREEMPT_RT
> patchset, are those concerns still valid or have they been sorted out?
>
> Please CC me on replies, I'm not subscribed to the list.

Do you have any use case for BPF + PREEMPT_RT ?  I am not a RT expert,
however, In my understanding, BPF + PREEMPT_RT in the vanilla kernel
basically can work togerther basically. The memory allocation concern is
partially resolved and there is still undergoing effort trying to
resolve it [1]. The up_read_non_owner problem has been avoided
explicitly and the non-preemptible context for bpf prog has also been
fixed. Although the running of test_maps and test_progs under PREEMPT_RT
report some problems, I think these problem could be fixed. As for v6.6,
I think it may be OK for BPF + PREEMPT_RT case.

[1]:
https://lore.kernel.org/bpf/20241210023936.46871-1-alexei.starovoitov@gmail.com/
> Thanks,
> Chris Friesen
>
>
> .