Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966180AbdIYUXt (ORCPT ); Mon, 25 Sep 2017 16:23:49 -0400 Received: from mga06.intel.com ([134.134.136.31]:45260 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966165AbdIYUXs (ORCPT ); Mon, 25 Sep 2017 16:23:48 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.42,437,1500966000"; d="scan'208";a="155319926" From: kan.liang@intel.com To: acme@kernel.org, peterz@infradead.org, mingo@redhat.com, linux-kernel@vger.kernel.org Cc: jolsa@kernel.org, namhyung@kernel.org, adrian.hunter@intel.com, lukasz.odzioba@intel.com, ak@linux.intel.com, Kan Liang Subject: [PATCH RFC V3 5/5] perf top: switch back to overwrite mode Date: Mon, 25 Sep 2017 13:23:08 -0700 Message-Id: <1506370988-56587-6-git-send-email-kan.liang@intel.com> X-Mailer: git-send-email 2.5.5 In-Reply-To: <1506370988-56587-1-git-send-email-kan.liang@intel.com> References: <1506370988-56587-1-git-send-email-kan.liang@intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2453 Lines: 61 From: Kan Liang perf_top__mmap_read has severe performance issue in Knights Landing/Mill, when monitoring in heavy load system. It costs several minutes to finish, which is unacceptable. perf top was overwrite mode. But it is changed to non overwrite mode since commit 93fc64f14472 ("perf top: Switch to non overwrite mode"). For non overwrite mode, it tries to read everything in the ring buffer and does not check the messup. Once there are lots of samples delivered shortly, the processing time could be very long. Knights Landing/Mill as a manycore processor contains a large number of small cores. Because of the huge core number, it will generated lots of samples in a heavy load system. Also, since the huge sample#, the mmap writer probably bite the tail and mess up the samples. Switching to overwrite mode, which dropping the unsure mmap entries, significantly speeds up the whole progress. Considering the real time requirement for perf top, it should switch back to overwrite mode. Only warning once if the messup is detected. Providing some hints to users. Signed-off-by: Kan Liang --- tools/perf/builtin-top.c | 2 +- tools/perf/util/evlist.c | 5 ++++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c index 477a869..4b4af34 100644 --- a/tools/perf/builtin-top.c +++ b/tools/perf/builtin-top.c @@ -902,7 +902,7 @@ static int perf_top__start_counters(struct perf_top *top) } } - if (perf_evlist__mmap(evlist, opts->mmap_pages, false) < 0) { + if (perf_evlist__mmap(evlist, opts->mmap_pages, true) < 0) { ui__error("Failed to mmap with %d (%s)\n", errno, str_error_r(errno, msg, sizeof(msg))); goto out_err; diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 6a0d7ff..ef0b6b1 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -723,7 +723,10 @@ perf_mmap__read(struct perf_mmap *md, bool check_messup, u64 start, * In either case, truncate and restart at 'end'. */ if (diff > md->mask / 2 || diff < 0) { - fprintf(stderr, "WARNING: failed to keep up with mmap data.\n"); + WARN_ONCE(1, "WARNING: failed to keep up with mmap data.\n" + "Please try increasing the period (-c) or\n" + "decreasing the freq (-F) or\n" + "limiting the number of CPUs"); /* * 'end' points to a known good entry, start there. -- 2.5.5