From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 EE460256C61 for ; Wed, 17 Dec 2025 05:12:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765948377; cv=none; b=dG+uA5rmya2pHz2piXqeMTksRKOLT+3DIWSDDTg630RBaQkjMXwdElx3SPunPOyZemiiM4j/l31jrWFDGW5VGxjS/A7BlybNYHe6ECW+ZNwCsDmcf3eTXTKGtcl8cNa6bWzE3+lUWoyJvZzCj69QzG7Oohyk5O8GWtlqE0LbfAw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765948377; c=relaxed/simple; bh=aRLI+YqwVHMF3D0VslZGuO+RkAm0zwioigHPwY9Ks40=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=CAkU7OW0ddVOO8qhwgwj3mSGx8ecMc25AXNCco6o9/cSX9R/0mgoh0e3xJy58JjASiiY7DGQE8QQDvDzDuyC7i38TidU4XhxJ1uuxP1efMiTClCvm1zUpqx/m5dfwt71UBikjrCBLoVKpF2bpyqMEY0d9JLaNP9s3Sj+9WRmq1Q= 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=VEGC0JhL; arc=none smtp.client-ip=91.218.175.174 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="VEGC0JhL" 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=1765948363; 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=x+G9R0iiLndyw6ppk44l1debId7zW9u7tSzJlQEKdiE=; b=VEGC0JhLdSqY2QZuIP62G5qQSlaXO0LyWGKDo5cUae6mBLF5UonK4uEhh6LaM7+5NmKjHO iDToIq+9Bv+KqZDBn6whNitpYSEeMqajESC0Ihi72LwYpf4weshUam5zbvIglCf5YJ/GdN +VCizlOGff22pfjsK+k+w/ZAg3x6ShA= 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 v7 0/2] Pass external callchain entry to get_perf_callchain Date: Wed, 17 Dec 2025 13:12:00 +0800 Message-ID: <20251217051203.1738517-1-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 - v6 -> v7: From yonghong - Add ack in patch2 - v6: https://lore.kernel.org/bpf/20251112163148.100949-1-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