From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 10CE027FD52 for ; Mon, 13 Oct 2025 17:48:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760377690; cv=none; b=U1t79aNaANkIEn5PbCtMNChpjXVX5nGUpVQ+H5uyWKH3j1OSp/a7t0a+Q5OL/M79cHz6oDgCTjLVVLs/1phzwQ/f2hCuyB29eEinvI64DU7ZGFGJhUesYHq/d/3ak03hYhnPPxyPmm3O5ZMZGmFod8lErguXunvaj0aglXvdu1E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760377690; c=relaxed/simple; bh=Fz2Z0NVg/DpxS1jweNIyZgePAu4cm4J9w/NK89KwvTo=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=PRRWTICq29A6VVEX5u9zC09BQJ3G2mAKvv+uzM2Ggx9F9rd5+GyB/fpCIBHN9i9rOVX+AOr9faWgXQDE8b8rjkX12ktm9G2Q4sQl3un+Kkr5XPVyqc4qjYJyXtk3Di2vQMj9vnO/xSf1/V2ZqUHI34aZjfk0Q9ZGK7pwBF3E+dQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=VxzJxKIC; arc=none smtp.client-ip=91.218.175.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="VxzJxKIC" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1760377675; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=dQog++Z4DABPXGobwnLJdN42FYEo1zhiAYhURAKlFOI=; b=VxzJxKICuu2V++rKVk+ZLlHlcziBjDWagVThwUkaCtfBN/Y7aJ0ivBFRXpZz05k6xpy8c5 xR4H4gPdQuOcUUiTsAeWifhnn4AV1wthnL304+12V5T7qzviNz329dKXh4BjsI7Q4e5pZd keogQh+6AEcYloTIOsY1Y3ZrscMkOnk= From: Tao Chen To: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, 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 Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Tao Chen Subject: [PATCH bpf-next RFC 0/2] Pass external callchain entry to get_perf_callchain Date: Tue, 14 Oct 2025 01:47:19 +0800 Message-ID: <20251013174721.2681091-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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 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