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From:   kan.liang@intel.com
To:     acme@kernel.org, peterz@infradead.org, mingo@redhat.com,
        linux-kernel@vger.kernel.org
Cc:     wangnan0@huawei.com, jolsa@kernel.org, namhyung@kernel.org,
        ak@linux.intel.com, yao.jin@linux.intel.com,
        Kan Liang <kan.liang@intel.com>
Subject: [PATCH V5 17/17] perf top: check the latency of perf_top__mmap_read()
Date:   Thu, 18 Jan 2018 13:26:32 -0800
Message-Id: <1516310792-208685-18-git-send-email-kan.liang@intel.com>
In-Reply-To: <1516310792-208685-1-git-send-email-kan.liang@intel.com>
References: <1516310792-208685-1-git-send-email-kan.liang@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
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From: Kan Liang <kan.liang@intel.com>

The latency of perf_top__mmap_read should be lower than refresh time.
If not, give some hints to reduce the latency.

Signed-off-by: Kan Liang <kan.liang@intel.com>
---
 tools/perf/builtin-top.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 465a699..79ed39f 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -889,8 +889,10 @@ static void perf_top__mmap_read(struct perf_top *top)
 {
 	bool overwrite = top->record_opts.overwrite;
 	struct perf_evlist *evlist = top->evlist;
+	unsigned long long start, end;
 	int i;
 
+	start = rdclock();
 	if (overwrite)
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_DATA_PENDING);
 
@@ -901,6 +903,13 @@ static void perf_top__mmap_read(struct perf_top *top)
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_EMPTY);
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
 	}
+	end = rdclock();
+
+	if ((end - start) > (unsigned long long)top->delay_secs * NSEC_PER_SEC)
+		ui__warning("Too slow to read ring buffer.\n"
+			    "Please try increasing the period (-c) or\n"
+			    "decreasing the freq (-F) or\n"
+			    "limiting the number of CPUs (-C)\n");
 }
 
 /*
-- 
2.5.5