Re: [PATCH bpf-next RFC 0/2] Pass external callchain entry to get_perf_callchain

Jiri Olsa
2025-10-13T20:41:29Z

On Tue, Oct 14, 2025 at 01:47:19AM +0800, Tao Chen wrote:
> Background
> ==========
> Alexei noted we should use preempt_disable to protect get_perf_callchain
> in bpf stackmap.
> https://lore.kernel.org/bpf/CAADnVQ+s8B7-fvR1TNO-bniSyKv57cH_ihRszmZV7pQDyV=VDQ@mail.gmail.com
>
> A previous patch was submitted to attempt fixing this issue. And Andrii
> suggested teach get_perf_callchain to let us pass that buffer directly to
> avoid that unnecessary copy.
> https://lore.kernel.org/bpf/20250926153952.1661146-1-chen.dylane@linux.dev
>
> Proposed Solution
> =================
> Add external perf_callchain_entry parameter for get_perf_callchain to
> allow us to use external buffer from BPF side. The biggest advantage is
> that it can reduce unnecessary copies.
>
> Todo
> ====
> If the above changes are reasonable, it seems that get_callchain_entry_for_task
> could also use an external perf_callchain_entry.
>
> But I'm not sure if this modification is appropriate. After all, the
> implementation of get_callchain_entry in the perf subsystem seems much more
> complex than directly using an external buffer.
>
> Comments and suggestions are always welcome.
>
> Tao Chen (2):
> perf: Use extern perf_callchain_entry for get_perf_callchain
> bpf: Pass external callchain entry to get_perf_callchain

hi,
I can't get this applied on bpf-next/master, what do I miss?

thanks,
jirka

>
> include/linux/perf_event.h | 5 +++--
> kernel/bpf/stackmap.c | 19 +++++++++++--------
> kernel/events/callchain.c | 18 ++++++++++++------
> kernel/events/core.c | 2 +-
> 4 files changed, 27 insertions(+), 17 deletions(-)
>
> --
> 2.48.1
>