linux-kernel - [PATCH] perf record: Change warning for missing sysfs entry to debug

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Date:   Thu, 12 Apr 2018 15:32:46 +0200
From:   Thomas Richter <tmricht@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Cc:     brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, Thomas Richter <tmricht@...ux.ibm.com>
Subject: [PATCH] perf record: Change warning for missing sysfs entry to debug

Using perf on 4.16.0 kernel on s390 shows warning
   failed: can't open node sysfs data
each time I run command perf record ... for example:

[root@...lp76 perf]# ./perf record -e rB0000 -- sleep 1
[ perf record: Woken up 1 times to write data ]
failed: can't open node sysfs data
[ perf record: Captured and wrote 0.001 MB perf.data (4 samples) ]
[root@...lp76 perf]#

It turns out commit e2091cedd51bf ("perf tools: Add MEM_TOPOLOGY
feature to perf data file") tries to open directory named
/sys/devices/system/node/ which does not exist on s390.

This is the call stack:
 __cmd_record
 +---> perf_session__write_header
       +---> perf_header__adds_write
             +---> do_write_feat
	           +---> write_mem_topology
		         +---> build_mem_topology
			       prints warning
The issue starts in do_write_feat() which unconditionally
loops over all features and now includes HEADER_MEM_TOPOLOGY and calls
write_mem_topology().
Function record__init_features() at the beginning of __cmd_record()
sets all features and then turns off some of them.

Fix this by changing the warning to a level 2 debug output statement.
So it is only shown when debug level 2 or higher is set.

Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
---
 tools/perf/util/header.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 121df1683c36..a8bff2178fbc 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1320,7 +1320,8 @@ static int build_mem_topology(struct memory_node *nodes, u64 size, u64 *cntp)
 
 	dir = opendir(path);
 	if (!dir) {
-		pr_warning("failed: can't open node sysfs data\n");
+		pr_debug2("%s: could't read %s, does this arch have topology information?\n",
+			  __func__, path);
 		return -1;
 	}
 
-- 
2.14.3