From patchwork Thu Sep 12 18:14:01 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Reinette Chatre X-Patchwork-Id: 13802415 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.21]) (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 315411C1ADB; Thu, 12 Sep 2024 18:05:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.21 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726164302; cv=none; b=OatqNx7ukvtCwLlWoaSfNG6nBkfr8UY51SyyK/nq2iEm4oHB4HrtlSlMX6rWOhHtLmTyGDNsZqML86WGmOs8iRY+35WGtTo8Gy8SPNVTiE9aJFk+BsOFkcEtsPp+p2GD47Ihsc+ha9s3UyG8sipAE8XvRFUQDepn1z8GCbyhRds= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726164302; c=relaxed/simple; bh=92pWei0aQ4YO4Oh0M7RHrJb9MqFXjLiYkf/YT5NhMKs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=p1gJWpwUSR4+0iWwOZu7qvUboKI6Ml2uI8TIwlkWP6NtMHsihmQccSkcigq6Ij0DDnQYe8kxredZfL+aeq4weEEhhfyAVUGUw6AyGsimjuNcDFNHgNRUMPCWg/lHXtj23YmYcOoTbCrdFFEpRS8dS3h9npH54kqa0/auAR0jQEM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=JRQzbvXY; arc=none smtp.client-ip=198.175.65.21 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="JRQzbvXY" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1726164302; x=1757700302; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=92pWei0aQ4YO4Oh0M7RHrJb9MqFXjLiYkf/YT5NhMKs=; b=JRQzbvXY8eCs6gfyjaGTvoxSV/fEWQ3kUtkZYHcMWYmw+3Nn3+ar4qNb YK39ctB/BTDHyxeQJ4M7pQ0jP2tcA65WVDCu0uwqMDphVprspWPyHEvw+ 78wnFBrJysJjTpwUg94j9th1zLbc7pFJcdJrx3q0tshZG3twz98YmjTJ3 VTXwt9/pdPWMssjGpzdvLJqgjMwLe/ejbiheD/oRRJGgmMMP8+9nofCIx ROKFwCoi/Mpr4zfWXzvGnsrHTWaeLha7tX74kQuC5V/0tdFVBaI+FaYAF FC/6eJ9foOBGJgxnpBptYKTSUccUV39D7Q7GvqKQuRX+LeUIIMDlRDyEb Q==; X-CSE-ConnectionGUID: 74PYGfd4RE6+Nkha28MKOw== X-CSE-MsgGUID: Uw/XXcVEQQC701K1FWQXiQ== X-IronPort-AV: E=McAfee;i="6700,10204,11193"; a="24976622" X-IronPort-AV: E=Sophos;i="6.10,223,1719903600"; d="scan'208";a="24976622" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by orvoesa113.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Sep 2024 11:04:53 -0700 X-CSE-ConnectionGUID: ZiVBzlxSRm+jOdQGOKhWCQ== X-CSE-MsgGUID: +T/cSBSIRB2BdH1KvBu/GA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.10,223,1719903600"; d="scan'208";a="67724633" Received: from b04f130c85c0.jf.intel.com (HELO rchatre-desk1.jf.intel.com) ([10.165.154.99]) by orviesa009-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Sep 2024 11:04:53 -0700 From: Reinette Chatre To: fenghua.yu@intel.com, shuah@kernel.org, tony.luck@intel.com, peternewman@google.com, babu.moger@amd.com, ilpo.jarvinen@linux.intel.com Cc: maciej.wieczor-retman@intel.com, reinette.chatre@intel.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH V2 12/13] selftests/resctrl: Do not compare performance counters and resctrl at low bandwidth Date: Thu, 12 Sep 2024 11:14:01 -0700 Message-ID: <955545d3377afc359d7b8b3915455bfdfc0d6605.1726164080.git.reinette.chatre@intel.com> X-Mailer: git-send-email 2.46.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The MBA test incrementally throttles memory bandwidth, each time followed by a comparison between the memory bandwidth observed by the performance counters and resctrl respectively. While a comparison between performance counters and resctrl is generally appropriate, they do not have an identical view of memory bandwidth. For example RAS features or memory performance features that generate memory traffic may drive accesses that are counted differently by performance counters and MBM respectively, for instance generating "overhead" traffic which is not counted against any specific RMID. As a ratio, this different view of memory bandwidth becomes more apparent at low memory bandwidths. It is not practical to enable/disable the various features that may generate memory bandwidth to give performance counters and resctrl an identical view. Instead, do not compare performance counters and resctrl view of memory bandwidth when the memory bandwidth is low. Bandwidth throttling behaves differently across platforms so it is not appropriate to drop measurement data simply based on the throttling level. Instead, use a threshold of 750MiB that has been observed to support adequate comparison between performance counters and resctrl. Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen --- Changes since V1: - Fix code alignment and spacing. - Modify flow to use "continue" instead of "break" now that earlier changes decreases throttling. - Expand comment of define to elaborate causes of discrepancy between performance counters and MBM. --- tools/testing/selftests/resctrl/mba_test.c | 7 +++++++ tools/testing/selftests/resctrl/resctrl.h | 10 ++++++++++ 2 files changed, 17 insertions(+) diff --git a/tools/testing/selftests/resctrl/mba_test.c b/tools/testing/selftests/resctrl/mba_test.c index d8d9637c1951..5c6063d0a77c 100644 --- a/tools/testing/selftests/resctrl/mba_test.c +++ b/tools/testing/selftests/resctrl/mba_test.c @@ -98,6 +98,13 @@ static bool show_mba_info(unsigned long *bw_imc, unsigned long *bw_resc) avg_bw_imc = sum_bw_imc / (NUM_OF_RUNS - 1); avg_bw_resc = sum_bw_resc / (NUM_OF_RUNS - 1); + if (avg_bw_imc < THROTTLE_THRESHOLD || avg_bw_resc < THROTTLE_THRESHOLD) { + ksft_print_msg("Bandwidth below threshold (%d MiB). Dropping results from MBA schemata %u.\n", + THROTTLE_THRESHOLD, + ALLOCATION_MIN + ALLOCATION_STEP * allocation); + continue; + } + avg_diff = (float)labs(avg_bw_resc - avg_bw_imc) / avg_bw_imc; avg_diff_per = (int)(avg_diff * 100); diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h index dc01dc75cba5..eb151ac74938 100644 --- a/tools/testing/selftests/resctrl/resctrl.h +++ b/tools/testing/selftests/resctrl/resctrl.h @@ -43,6 +43,16 @@ #define DEFAULT_SPAN (250 * MB) +/* + * Memory bandwidth (in MiB) below which the bandwidth comparisons + * between iMC and resctrl are considered unreliable. For example RAS + * features or memory performance features that generate memory traffic + * may drive accesses that are counted differently by performance counters + * and MBM respectively, for instance generating "overhead" traffic which + * is not counted against any specific RMID. + */ +#define THROTTLE_THRESHOLD 750 + /* * fill_buf_param: "fill_buf" benchmark parameters * @buf_size: Size (in bytes) of buffer used in benchmark.