From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 2BF614E3246; Thu, 17 Sep 2026 15:33:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789659191; cv=none; b=iG2Pt1V7aCs9ao2/8ahIih6L+qHeQi4ep4k8dMd3clm6+VuMMQ17PBZO44F4Q2f+HmeVTp5SzQZ7mt3Unr8IuABVql/Hjfn7YzP1RW8EQtbClEvkkJG+Z1XKPJd1I3Mjavqg1U3GKM64M3R59c8v9fsmb7HB0PqSqTpLUs+VFyM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789659191; c=relaxed/simple; bh=eK1lEcFgkaNthxd7fNwc7CoqYQrSTW2okBNnTIRYYPQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Av74p2kObl97xweKac6+s9FIOCE5wVif8zpTc7f0ucHXJZ5L2ZvBJ5o279vH6Nd8a7rL9CdOjZmwqLeegBj0QFHyg5TCxHfU52Y3lUd4NeJDZFhVZCUy857gjnoAy/xHV59ABiLx1arWAbvLpDOVQVpMeeO6VzTVZ50WN6ahVfc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=SL4qYGmh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="SL4qYGmh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CFC141F00893; Thu, 17 Sep 2026 15:33:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789659182; bh=WA8UnWMF5yDQBHxHYeWeK2NOB+L4phxgwKp0FpR1RWU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=SL4qYGmhEIsOmZyhLADYvQ4NVFRQhA6F0gKvo+5MZs8U8wAOBrG6pLOFj3S7oSNc7 MGSmR8VW35ANBlAtuq7HaMHEdp/XZnGOjlLA/MREc2lZK1iKZ1rt1t+1ROkW5mWMdi apaL75gCGq/PZhy83Vpm7sU6H6UPlnlaqkaaebu4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Tamas Petz , Leo Yan , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 7.2 172/733] perf/core: Skip empty AUX records with only format flags Date: Thu, 17 Sep 2026 16:08:00 +0100 Message-ID: <20260917151355.389329485@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151350.597953846@linuxfoundation.org> References: <20260917151350.597953846@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Leo Yan [ Upstream commit 8a7f5b5e860b5c113ca99acd5b1e9074f5c5af3c ] perf_aux_output_end() emits a PERF_RECORD_AUX when the recorded size is nonzero or when any flag other than PERF_AUX_FLAG_OVERWRITE is set. PMU format flags describe how an AUX payload is encoded. TRBE driver sets PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW for raw trace buffers, causing an AUX record to be emitted even when no trace data. This is noticeable when tracing a task with strace. Ptrace stops repeatedly end empty AUX transactions, producing many zero-sized PERF_RECORD_AUX records. For example: perf record -e cs_etm//u -m,128M -- strace ls perf script -D 2>&1 | awk '/PERF_RECORD_AUX offset/ { for (i = 1; i <= NF; i++) if ($i == "size:" && $(i + 1) == "0") count++ } END { print count }' 165 This recording contains 165 zero-sized AUX records which provide no useful information to userspace. Ignore PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK, together with PERF_AUX_FLAG_OVERWRITE, when deciding whether an empty AUX record is useful. Zero-sized records carrying TRUNCATED, PARTIAL or COLLISION are still emitted. Fixes: 547b60988e63 ("perf: aux: Add flags for the buffer format") Reported-by: Tamas Petz Signed-off-by: Leo Yan Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20260825-perf_core_fix_zero_aux_records-v1-1-23b95e8d5df3@arm.com Signed-off-by: Sasha Levin --- kernel/events/ring_buffer.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 9fe92161715e0..1b1ffe0533e58 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -509,7 +509,10 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) /* * Only send RECORD_AUX if we have something useful to communicate * - * Note: the OVERWRITE records by themselves are not considered + * PMU_FORMAT bits identify the PMU type rather than an AUX event + * has occurred, so ignore them for zero-sized records. + * + * The OVERWRITE records by themselves are not considered * useful, as they don't communicate any *new* information, * aside from the short-lived offset, that becomes history at * the next event sched-in and therefore isn't useful. @@ -518,7 +521,9 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) * offset. So, from now on we don't output AUX records that * have *only* OVERWRITE flag set. */ - if (size || (handle->aux_flags & ~(u64)PERF_AUX_FLAG_OVERWRITE)) + if (size || + (handle->aux_flags & ~(u64)(PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK | + PERF_AUX_FLAG_OVERWRITE))) perf_event_aux_event(handle->event, aux_head, size, handle->aux_flags); -- 2.53.0