From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta0.migadu.com (out-184.mta0.migadu.com [91.218.175.184]) (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 963232EBBBD for ; Tue, 14 Oct 2025 10:01:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.184 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760436114; cv=none; b=oCren2/eJiH7sjqz1ibNbYEMFjebk6e9tOkanFCSao6kFXzxyA6mptJ03A/KzzL+ZlSj+9li3VcCoO4rhd629mTMa9KOLTuXVjGXkJO2S5MxtEMZEhZ51UBPRiyPFnVa0ZvpemV/lgPi3Ov7jvO4iPzg4sDyum7qZU+xZVHG+QQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760436114; c=relaxed/simple; bh=//nKyMjQT/XUVl4ap1KlpQMlW3dQCozDjSt4HbI99YU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=W9tVUnQ9dNysVCApebHQfjqsXdwjNF5vKdBIj7+kRXEYQw0QXYQsXA4muMeR8D9sdBm4crrsMBarxUYIZ1SnTTEIazNtY2/02FZ3e3TCA5k24up3v/lLkmUValE/dsYCSo0HGP4ANprRPYTiQHLj3n0iugzzLvvbNmlHQWHv2tU= 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=vF3gWFMA; arc=none smtp.client-ip=91.218.175.184 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="vF3gWFMA" 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=1760436109; 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=sbDoAjrS2xAf/gutlRdmjLlBlDoaX2SKsgUsS0O9aH0=; b=vF3gWFMAiQfPe6tldLH2jPEuTzyo9XPBip1DGJPnV0xLBgGR3vXUggKZTeYpUzfNx1jFlH GfqzaR0EqenXw1C66Jdnwrb2v1dPgrcUfU6co1XGPKJbRkcMGrOjBduFCmrzA49vIQa5As EX1tBTO3LR8UoqsLAQdQYX+3d7lzOds= 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 v2 0/2] Pass external callchain entry to get_perf_callchain Date: Tue, 14 Oct 2025 18:01:26 +0800 Message-ID: <20251014100128.2721104-1-chen.dylane@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-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 confict - v1: https://lore.kernel.org/bpf/20251013174721.2681091-1-chen.dylane@linux.dev 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 | 4 ++-- kernel/bpf/stackmap.c | 19 +++++++++++-------- kernel/events/callchain.c | 13 +++++++++---- kernel/events/core.c | 2 +- 4 files changed, 23 insertions(+), 15 deletions(-) -- 2.48.1