[PATCH] cyclictest: stop any tracing after hitting a breaktrace threshold

[Clark Williams]

John,

This patch is against the devel/v0.98 branch. It turns off tracing in the 
tracemark() so that we don't lose information about what was going on when we 
hit the latency:


The current logic of using --tracemark and --notrace works for running
cyclictest with trace-cmd, but even if we are not doing any trace
manipulation in cyclictest, we still need to stop tracing when we hit a
breaktrace threshold (i.e. -b <n>).

Modify startup logic to hold open file descriptors for the tracemark file
*and* the tracing_on file. When we hit a threshold and call the tracemark()
function, write the marker to the trace buffers and then write a "0\n" to
the tracing_on file to turn off tracing, otherwise we lose the information
immediately prior to the point where we hit the latency.

Signed-off-by: Clark Williams <willi...@redhat.com>
---
 src/cyclictest/cyclictest.c | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/src/cyclictest/cyclictest.c b/src/cyclictest/cyclictest.c
index 902167010416..00e5f3d59a5b 100644
--- a/src/cyclictest/cyclictest.c
+++ b/src/cyclictest/cyclictest.c
@@ -489,7 +489,12 @@ static void tracemark(char *fmt, ...)
        va_start(ap, fmt);
        len = vsnprintf(tracebuf, TRACEBUFSIZ, fmt, ap);
        va_end(ap);
+
+       /* write the tracemark message */
        write(tracemark_fd, tracebuf, len);
+
+       /* now stop any trace */
+       write(trace_fd, "0\n", 2);
 }
 
 
@@ -535,13 +540,28 @@ static void open_tracemark_fd(void)
 {
        char path[MAX_PATH];
 
-       if (tracemark_fd >= 0)
-               return;
+       /*
+        * open the tracemark file if it's not already open
+        */
+       if (tracemark_fd < 0) {
+               sprintf(path, "%s/%s", fileprefix, "trace_marker");
+               tracemark_fd = open(path, O_WRONLY);
+               if (tracemark_fd < 0) {
+                       warn("unable to open trace_marker file: %s\n", path);
+                       return;
+               }
+       }
 
-       sprintf(path, "%s/%s", fileprefix, "trace_marker");
-       tracemark_fd = open(path, O_WRONLY);
-       if (tracemark_fd < 0)
-               warn("unable to open trace_marker file: %s\n", path);
+       /*
+        * if we're not tracing and the tracing_on fd is not open,
+        * open the tracing_on file so that we can stop the trace
+        * if we hit a breaktrace threshold
+        */
+       if (notrace && trace_fd < 0) {
+               sprintf(path, "%s/%s", fileprefix, "tracing_on");
+               if ((trace_fd = open(path, O_WRONLY)) < 0)
+                       warn("unable to open tracing_on file: %s\n", path);
+       }
 }
 
 static void debugfs_prepare(void)
-- 
2.5.5

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