From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (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 CBD7C1CF8B; Mon, 26 Jan 2026 07:44:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769413490; cv=none; b=bD0whIaz3CAWyN2HA/LuduxoLckqZEPka16XRBdaTzVwFjO0geUJY7WqX5qzHDfkuzCaP4FottFaK4U0Od76iUV41FI+r72fb4JVMe+RDzMqGg9IqaSfLDhLB0QNxwr1OLm0ruhdzZ8R8S2O7lOOjvb+5svdtfcqsgstjjhwexg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769413490; c=relaxed/simple; bh=ii48tRw2ZR9B6/7Txp86uIm0OfcNEuYrC/eBBOAxMN0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=VRSvusIXGKPjg6AOSAdkBlYM/20dgrXzlhuExnnbVO/t2aXpP/RLBQh3XR1jOZQlqCTop71FXSMOHPMjatJ4V2MfzmfoGtEuyFM3rQf+hjkAIoN0mEkc3Cyi3pujBU71sQ/lsQ7AFtrqicUJastM880nMB3yzQv8Wx/e4EPto1c= 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=G7V5280r; arc=none smtp.client-ip=95.215.58.182 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="G7V5280r" 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=1769413476; 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=li9UX981rBOVQZW+/MvOTdHHTmm4jFDDc2r8HqCxVNs=; b=G7V5280rbfbLGwWj6tiiT/0K3B9LFnCHA321Vh8b5KqaoXIAkTOrOB2YCq1Gd6XrrF9jGm /0UJXqjXw+yl/FYOknW5DWdi+xkfaFkhxLqOtHWSxq34uYj0THYaB9m2+8a1NJmWgnTYxi lhCspFAn19fAlZz/YdYBu+9P4GBT3NA= 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 v8 0/3] Pass external callchain entry to get_perf_callchain Date: Mon, 26 Jan 2026 15:43:28 +0800 Message-ID: <20260126074331.815684-1-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 ==== 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 From AI - resolve conflict - v6: https://lore.kernel.org/bpf/20251112163148.100949-1-chen.dylane@linux.dev - v7 -> v8: From Andrii - Record rctx in perf_callchain_entry in patch1 - Export __get_perf_callchain in patch2 - v7: https://lore.kernel.org/bpf/20251217093326.1745307-1-chen.dylane@linux.dev Tao Chen (3): perf: Add rctx in perf_callchain_entry perf: Refactor get_perf_callchain bpf: Hold ther perf callchain entry until used completely include/linux/perf_event.h | 10 +++++-- kernel/bpf/stackmap.c | 58 ++++++++++++++++++++++++++++++------- kernel/events/callchain.c | 59 ++++++++++++++++++++++++-------------- 3 files changed, 93 insertions(+), 34 deletions(-) -- 2.48.1