From patchwork Fri Dec 15 15:05:06 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: =?utf-8?q?Ilpo_J=C3=A4rvinen?= X-Patchwork-Id: 754717 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.12]) (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 726DD3EA8E; Fri, 15 Dec 2023 15:08:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=linux.intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="Cdbvvknn" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1702652920; x=1734188920; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=c56pSutKyBL/+RSgpalm2vDnnz/5q/Fld2dkSwdn0Jk=; b=CdbvvknnhcTxeFLKzOr6+zJk3q6dOn7PR47UUqyhS1n4rAuoEDkXlS1T +JNhxMXeolUg8FXrC2r0pm3M/mM2r/S058+4bVeCDjodhv+t3biG2ht9n TOzxS55b46ZHNcVLQQaGZC+c2YDrTkv3PydPhPd1kCA2cBOxGzCeMKxWG 1RhJ7jT4Qo7Cdfa9C7oGfXpco3UL4yK2p0KqME+C6q+KSYig8TElFvBvd PDW5O2qaZPeAZGg5gluQSsIbCVtYxA5K++K9TkvDxTXrmFTsz00BF8GmE ln1rBQRBHflPFUVUV/5aTx6lla+h28ONSegQ3SYmc/AwNp6VucU+o32Vi Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10924"; a="2453898" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="2453898" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by orvoesa104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 07:08:39 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10924"; a="809001431" X-IronPort-AV: E=Sophos;i="6.04,279,1695711600"; d="scan'208";a="809001431" Received: from ijarvine-desk1.ger.corp.intel.com (HELO localhost) ([10.246.49.116]) by orsmga001-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Dec 2023 07:08:35 -0800 From: =?utf-8?q?Ilpo_J=C3=A4rvinen?= To: linux-kselftest@vger.kernel.org, Reinette Chatre , Shuah Khan , Shaopeng Tan , =?utf-8?q?Maciej_Wiecz=C3=B3r-R?= =?utf-8?q?etman?= , Fenghua Yu Cc: linux-kernel@vger.kernel.org, =?utf-8?q?Ilpo_J=C3=A4rvinen?= Subject: [PATCH v4 20/29] selftests/resctrl: Replace file write with volatile variable Date: Fri, 15 Dec 2023 17:05:06 +0200 Message-Id: <20231215150515.36983-21-ilpo.jarvinen@linux.intel.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20231215150515.36983-1-ilpo.jarvinen@linux.intel.com> References: <20231215150515.36983-1-ilpo.jarvinen@linux.intel.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 The fill_buf code prevents compiler optimizating the entire read loop away by writing the final value of the variable into a file. While it achieves the goal, writing into a file requires significant amount of work within the innermost test loop and also error handling. A simpler approach is to take advantage of volatile. Writing through a pointer to a volatile variable is enough to prevent compiler from optimizing the write away, and therefore compiler cannot remove the read loop either. Add a volatile 'value_sink' into resctrl_tests.c and make fill_buf to write into it. As a result, the error handling in fill_buf.c can be simplified. Signed-off-by: Ilpo Järvinen Reviewed-by: Reinette Chatre --- v3: - Altered changelog's wording to not say "a volatile pointer" --- tools/testing/selftests/resctrl/fill_buf.c | 26 ++++--------------- tools/testing/selftests/resctrl/resctrl.h | 7 +++++ .../testing/selftests/resctrl/resctrl_tests.c | 4 +++ 3 files changed, 16 insertions(+), 21 deletions(-) diff --git a/tools/testing/selftests/resctrl/fill_buf.c b/tools/testing/selftests/resctrl/fill_buf.c index 635f938b11f0..8fe9574db9d8 100644 --- a/tools/testing/selftests/resctrl/fill_buf.c +++ b/tools/testing/selftests/resctrl/fill_buf.c @@ -78,10 +78,9 @@ static void fill_one_span_write(unsigned char *buf, size_t buf_size) } } -static int fill_cache_read(unsigned char *buf, size_t buf_size, bool once) +static void fill_cache_read(unsigned char *buf, size_t buf_size, bool once) { int ret = 0; - FILE *fp; while (1) { ret = fill_one_span_read(buf, buf_size); @@ -90,26 +89,16 @@ static int fill_cache_read(unsigned char *buf, size_t buf_size, bool once) } /* Consume read result so that reading memory is not optimized out. */ - fp = fopen("/dev/null", "w"); - if (!fp) { - ksft_perror("Unable to write to /dev/null"); - return -1; - } - fprintf(fp, "Sum: %d ", ret); - fclose(fp); - - return 0; + *value_sink = ret; } -static int fill_cache_write(unsigned char *buf, size_t buf_size, bool once) +static void fill_cache_write(unsigned char *buf, size_t buf_size, bool once) { while (1) { fill_one_span_write(buf, buf_size); if (once) break; } - - return 0; } static unsigned char *alloc_buffer(size_t buf_size, int memflush) @@ -143,21 +132,16 @@ static unsigned char *alloc_buffer(size_t buf_size, int memflush) int run_fill_buf(size_t buf_size, int memflush, int op, bool once) { unsigned char *buf; - int ret; buf = alloc_buffer(buf_size, memflush); if (!buf) return -1; if (op == 0) - ret = fill_cache_read(buf, buf_size, once); + fill_cache_read(buf, buf_size, once); else - ret = fill_cache_write(buf, buf_size, once); + fill_cache_write(buf, buf_size, once); free(buf); - if (ret) { - printf("\n Error in fill cache\n"); - return -1; - } return 0; } diff --git a/tools/testing/selftests/resctrl/resctrl.h b/tools/testing/selftests/resctrl/resctrl.h index f22b7897251e..5b9bea505120 100644 --- a/tools/testing/selftests/resctrl/resctrl.h +++ b/tools/testing/selftests/resctrl/resctrl.h @@ -78,6 +78,13 @@ struct perf_event_read { #define CMT_STR "cmt" #define CAT_STR "cat" +/* + * Memory location that consumes values compiler must not optimize away. + * Volatile ensures writes to this location cannot be optimized away by + * compiler. + */ +extern volatile int *value_sink; + extern pid_t bm_pid, ppid; extern char llc_occup_path[1024]; diff --git a/tools/testing/selftests/resctrl/resctrl_tests.c b/tools/testing/selftests/resctrl/resctrl_tests.c index 2bbe3045a018..f0d573aa363b 100644 --- a/tools/testing/selftests/resctrl/resctrl_tests.c +++ b/tools/testing/selftests/resctrl/resctrl_tests.c @@ -10,6 +10,10 @@ */ #include "resctrl.h" +/* Volatile memory sink to prevent compiler optimizations */ +static volatile int sink_target; +volatile int *value_sink = &sink_target; + static int detect_vendor(void) { FILE *inf = fopen("/proc/cpuinfo", "r");