From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta1.migadu.com (out-181.mta1.migadu.com [95.215.58.181]) (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 A02172550AF for ; Wed, 12 Nov 2025 16:32:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762965139; cv=none; b=OL3p++nbVelrRH7EZFy3FkrymnlrKDqocOWiMjtncJ3Q+smx3jY/xJYyTYrNBIgz4fnX8XT61fMv1VHUNMTGo7R8FL7FhWN1GzOFESCygy2ya5NTuLrKTKqeqf7Hww5Rk6+UdT/CzpRlQgQzLhCZYweppw1YazPFExFJBm2M2vc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762965139; c=relaxed/simple; bh=824HB0FwxXbrTkd2VprLbP8RIEvV0Ma1dBRa+Qdwaus=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=WwFxZYWtG4UxFekqa5z3N2pz272yfwLR7zJ76eNRd76XVgnGF9kFtkBwip3G5LFOHblQwo69vYyymeF0F0RRbBw9RdT3LcQlKDxZamjXQQBynm1d8w9JFMG+WyXoICV0+PCpyaUL2G6dizMM3Y1wheZTATqMkdrY5GaoVaHKksM= 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=TQb0quDZ; arc=none smtp.client-ip=95.215.58.181 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="TQb0quDZ" 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=1762965125; 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=2SvTyG20gTI6PLA4Qy0uxk1b8dqb6/aV5Fy9WbEByow=; b=TQb0quDZ8exl/W0BgAhk8oMQoZWO65M93a49bOynUQEKV9aze94ECS37o6ZFsdgQakB9ff iboEeIRhjv6iv374nRppYnGO71diDSL467/j7RKdUlleJpkdkHzjViqAoxZp2TeaFh90WI NDS7VZkcEWvRtG5Krgl7v+5jyaiYFBo= 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 Cc: linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Tao Chen Subject: [PATCH bpf-next v6 0/2] Pass external callchain entry to get_perf_callchain Date: Thu, 13 Nov 2025 00:31:46 +0800 Message-ID: <20251112163148.100949-1-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 ==== 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 - v3 -> v4: From Peter - refactor get_perf_callchain and add three new APIs to use perf callchain easily. From Andrii - reuse the perf callchain management. - rename patch1 and patch2. - v3: https://lore.kernel.org/bpf/20251019170118.2955346-1-chen.dylane@linux.dev - v4 -> v5: From Yonghong - keep add_mark false in stackmap when refactor get_perf_callchain in patch1. - add atomic operation in get_recursion_context in patch2. - rename bpf_put_callchain_entry with bpf_put_perf_callchain in patch3. - rebase bpf-next master. - v4: https://lore.kernel.org/bpf/20251028162502.3418817-1-chen.dylane@linux.dev - v5 -> v6: From Peter - disable preemption from BPF side in patch2. From AI - use ctx->entry->nr instead of ctx->nr in patch1. - v5: https://lore.kernel.org/bpf/20251109163559.4102849-1-chen.dylane@linux.dev Tao Chen (2): perf: Refactor get_perf_callchain bpf: Hold the perf callchain entry until used completely include/linux/perf_event.h | 9 +++++ kernel/bpf/stackmap.c | 67 +++++++++++++++++++++++++++------- kernel/events/callchain.c | 73 ++++++++++++++++++++++++-------------- 3 files changed, 111 insertions(+), 38 deletions(-) -- 2.48.1