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Mon, 13 Oct 2025 13:41:27 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 13 Oct 2025 22:41:19 +0200 To: Tao Chen Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, irogers@google.com, adrian.hunter@intel.com, kan.liang@linux.intel.com, song@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH bpf-next RFC 0/2] Pass external callchain entry to get_perf_callchain Message-ID: References: <20251013174721.2681091-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251013174721.2681091-1-chen.dylane@linux.dev> 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 >