[PATCH 1/3] tools/kvm_stat: add command line switch '-z' to skip zero records

[Stefan Raspl <raspl@xxxxxxxxxxxxx>]

From: Stefan Raspl <raspl@xxxxxxxxxx>

When running in logging mode, skip records with all zeros (=empty records)
to preserve space when logging to files.

Signed-off-by: Stefan Raspl <raspl@xxxxxxxxxxxxx>
---
 tools/kvm/kvm_stat/kvm_stat     | 47 +++++++++++++++++++++++++--------
 tools/kvm/kvm_stat/kvm_stat.txt |  4 +++
 2 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/tools/kvm/kvm_stat/kvm_stat b/tools/kvm/kvm_stat/kvm_stat
index 7fe767bd2625..54000ac508f9 100755
--- a/tools/kvm/kvm_stat/kvm_stat
+++ b/tools/kvm/kvm_stat/kvm_stat
@@ -1488,7 +1488,8 @@ def batch(stats):
 
 
 class StdFormat(object):
-    def __init__(self, keys):
+    def __init__(self, keys, skip_zero_records):
+        self._skip_zero_records = skip_zero_records
         self._banner = ''
         for key in keys:
             self._banner += key.split(' ')[0] + ' '
@@ -1496,16 +1497,21 @@ class StdFormat(object):
     def get_banner(self):
         return self._banner
 
-    @staticmethod
-    def get_statline(keys, s):
+    def get_statline(self, keys, s):
         res = ''
+        non_zero = False
         for key in keys:
+            if s[key].delta != 0:
+                non_zero = True
             res += ' %9d' % s[key].delta
+        if self._skip_zero_records and not non_zero:
+            return ''
         return res
 
 
 class CSVFormat(object):
-    def __init__(self, keys):
+    def __init__(self, keys, skip_zero_records):
+        self._skip_zero_records = skip_zero_records
         self._banner = 'timestamp'
         self._banner += reduce(lambda res, key: "{},{!s}".format(res,
                                key.split(' ')[0]), keys, '')
@@ -1513,8 +1519,14 @@ class CSVFormat(object):
     def get_banner(self):
         return self._banner
 
-    @staticmethod
-    def get_statline(keys, s):
+    def get_statline(self, keys, s):
+        if self._skip_zero_records:
+            non_zero = False
+            for key in keys:
+                if s[key].delta != 0:
+                    non_zero = True
+            if self._skip_zero_records and not non_zero:
+                return ''
         return reduce(lambda res, key: "{},{!s}".format(res, s[key].delta),
                       keys, '')
 
@@ -1523,14 +1535,20 @@ def log(stats, opts, frmt, keys):
     """Prints statistics as reiterating key block, multiple value blocks."""
     line = 0
     banner_repeat = 20
+    banner_printed = False
+
     while True:
         try:
             time.sleep(opts.set_delay)
-            if line % banner_repeat == 0:
+            if line % banner_repeat == 0 and not banner_printed:
                 print(frmt.get_banner())
-            print(datetime.now().strftime("%Y-%m-%d %H:%M:%S") +
-                  frmt.get_statline(keys, stats.get()))
+                banner_printed = True
+            statline = frmt.get_statline(keys, stats.get())
+            if len(statline) == 0:
+                continue
+            print(datetime.now().strftime("%Y-%m-%d %H:%M:%S") + statline)
             line += 1
+            banner_printed = False
         except KeyboardInterrupt:
             break
 
@@ -1651,9 +1669,16 @@ Press any other key to refresh statistics immediately.
                            default=False,
                            help='retrieve statistics from tracepoints',
                            )
+    argparser.add_argument('-z', '--skip-zero-records',
+                           action='store_true',
+                           default=False,
+                           help='omit records with all zeros in logging mode',
+                           )
     options = argparser.parse_args()
     if options.csv and not options.log:
         sys.exit('Error: Option -c/--csv requires -l/--log')
+    if options.skip_zero_records and not options.log:
+        sys.exit('Error: Option -z/--skip-zero-records requires -l/--log')
     try:
         # verify that we were passed a valid regex up front
         re.compile(options.fields)
@@ -1736,9 +1761,9 @@ def main():
     if options.log:
         keys = sorted(stats.get().keys())
         if options.csv:
-            frmt = CSVFormat(keys)
+            frmt = CSVFormat(keys, options.skip_zero_records)
         else:
-            frmt = StdFormat(keys)
+            frmt = StdFormat(keys, options.skip_zero_records)
         log(stats, options, frmt, keys)
     elif not options.once:
         with Tui(stats, options) as tui:
diff --git a/tools/kvm/kvm_stat/kvm_stat.txt b/tools/kvm/kvm_stat/kvm_stat.txt
index a97ded2aedad..24296dccc00a 100644
--- a/tools/kvm/kvm_stat/kvm_stat.txt
+++ b/tools/kvm/kvm_stat/kvm_stat.txt
@@ -104,6 +104,10 @@ OPTIONS
 --tracepoints::
         retrieve statistics from tracepoints
 
+*z*::
+--skip-zero-records::
+        omit records with all zeros in logging mode
+
 SEE ALSO
 --------
 'perf'(1), 'trace-cmd'(1)
-- 
2.17.1