From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta0.migadu.com (out-182.mta0.migadu.com [91.218.175.182]) (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 ECE62340DB0 for ; Tue, 21 Oct 2025 16:07:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761062823; cv=none; b=VSjl7DmY76PzbpmnITm1sxn49H2Naws9ZGIU/9SEzaYmay08sSkGuU/oR0f/OJVcFbXlr/blVagpm2esJmlM13wKgOBmLvjmETxBZUbn6s661TrMT9XweBSo5E7JYpCJ2C3q+pyTkUb3pv2h4mA3Lkv6hiGooEEB84XcwnnG/LY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761062823; c=relaxed/simple; bh=YPa1/94TURq8roxAhrQxuI18qIU9jr8OSUQ5t95QSdc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=haH4cuEfU4Z5dZB1C1Xb1E37O1ZBCroJu+HeKJqPMWyzFobycHD5ZZetalbI79cYB0clIhRsMwJp1WLL16Uk+0s6xkO7HWzGrhbiPz8Tt6ZEM+Nk6In6gbgT5Gm/gVYg2R4ZKcyt0119NsjPV4lBO61pOvH6YNEtyFQAzGtRXT8= 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=nVRnxNoj; arc=none smtp.client-ip=91.218.175.182 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="nVRnxNoj" 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=1761062808; 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=gKIHnWo1D+O0/tFKE4OrfXOjIB0Rx7n+Ag827XUFVcs=; b=nVRnxNojJUXxMfIe6tCF/T6+HbJIShaiqMPDWAej3Ron2l966jNcpOzD5bVan7Z7mlvLP1 TqI+O/5GRqLkL4eMF/bgyTwT1iQZz/qrSrRfK5K0tIFZm+Jw62rsd5XBwsBxQi8/Dhx7cU Ct1cq6NpZxRf7eHQa3bDrWNO9efL/ok= 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 v4 0/2] Pass external callchain entry to get_perf_callchain Date: Wed, 22 Oct 2025 00:06:31 +0800 Message-ID: <20251021160633.3046301-1-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 AI - fix double-put issue - v3: https://lore.kernel.org/bpf/4c35feba-e075-42c1-82c5-5589c16f088e@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 | 98 ++++++++++++++++++++++++++++---------- kernel/events/callchain.c | 13 +++-- kernel/events/core.c | 2 +- 4 files changed, 85 insertions(+), 32 deletions(-) -- 2.48.1