Re: [PATCH] bpf: Call cond_resched() to avoid soft lockup in trie_free()

[Matt Fleming]

On Wed, Jun 18, 2025 at 3:50 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> Do your homework pls.
> Set max_entries to 100G and report back.
> Then set max_entries to 1G _with_ cond_rescehd() hack and report back.

Hi,

I put together a small reproducer
https://github.com/xdp-project/bpf-examples/pull/130 which gives the
following results on an AMD EPYC 9684X 96-Core machine:

| Num of map entries | Linux 6.12.32 |  KASAN  | cond_resched |
|--------------------|---------------|---------|--------------|
| 1K                 | 0ms           | 4ms     | 0ms          |
| 10K                | 2ms           | 50ms    | 2ms          |
| 100K               | 32ms          | 511ms   | 32ms         |
| 1M                 | 427ms         | 5478ms  | 420ms        |
| 10M                | 5056ms        | 55714ms | 5040ms       |
| 100M               | 67253ms       | *       | 62630ms      |

* - I gave up waiting after 11.5 hours

Enabling KASAN makes the durations an order of magnitude bigger. The
cond_resched() patch eliminates the soft lockups with no effect on the
times.

Thanks,
Matt