From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta1.migadu.com (out-174.mta1.migadu.com [95.215.58.174]) (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 C27615227 for ; Sun, 19 Oct 2025 17:02:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760893344; cv=none; b=XaOZqjoDDiYWyTPIH3D88OprgG8EjwV1BkCRV9C9eDaJj3x3EJR/v+TK6XXxC+F0qs1a+J83NROXtJX2jVKHJcCCa8MDubsOtmmda0AAf652j4N366W9Q7BwF2Q3BKF+ZZCEx1W72PsjcyCaECYc7gXGa0IBcYtR3UB1djdeByY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760893344; c=relaxed/simple; bh=I4IPIkVRwwPljb/L00Berkh9PET7fL8xPobDbg7CT40=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=GtIfvokNXA0P2zHadCrqnjL/rcORwFby2PX6gBQZ30UZpwyPyZWyLmUqSypNJdqVJ+5+q/GHrlXDkJr9Trwh2OiF1RyAs/Nwg6kxc+xHqgzZBuojpHhlRji4OG5YUjuvAW7riuqMy+7s0kTrGwQfwkX1PZYBqMXotFoe7lJnlJA= 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=Ozh2bEuP; arc=none smtp.client-ip=95.215.58.174 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="Ozh2bEuP" 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=1760893330; 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=iqzfPOzTOCeOc2Nx+fmkWoPF6VmUZJ9IKHq9VTjuh08=; b=Ozh2bEuPujZu9hDHbL6X/MbypkfQeQapazzO2cXcJfqwe15DMWBnm/sM01+fiOiceHuznw pfabOMRhZ4TwMfgZ8GfWdimMjQ6nIpE07vN+9xdBj8Y3HtCOckGAv3tm6whSFFGp0ZXVNu OHPOdqPrF3Hn4HCpYjivoI293s5vh6Y= 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: [RFC PATCH bpf-next v3 0/2] Pass external callchain entry to get_perf_callchain Date: Mon, 20 Oct 2025 01:01:16 +0800 Message-ID: <20251019170118.2955346-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@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. Change list: - v1 -> v2 From Jiri - rebase code, fix conflict - v1: https://lore.kernel.org/bpf/20251013174721.2681091-1-chen.dylane@linux.dev - v2 -> v3: From Andrii - entries per CPU used in a stack-like fashion - v2: https://lore.kernel.org/bpf/20251014100128.2721104-1-chen.dylane@linux.dev Tao Chen (2): perf: Use extern perf_callchain_entry for get_perf_callchain bpf: Use per-cpu BPF callchain entry to save callchain include/linux/perf_event.h | 4 +- kernel/bpf/stackmap.c | 100 ++++++++++++++++++++++++++++--------- kernel/events/callchain.c | 13 +++-- kernel/events/core.c | 2 +- 4 files changed, 88 insertions(+), 31 deletions(-) -- 2.48.1