Re: [PATCH] cyclictest: stop any tracing after hitting a breaktrace threshold
From: Luiz Capitulino <hidden>
Date: 2016-05-03 19:56:49
Also in:
lkml
On Tue, 3 May 2016 12:59:53 -0500 Clark Williams [off-list ref] wrote:
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>).
Does it solve the problem for you if you revert ba4dd1bf54 and start cyclictest with: # cyclictest [...] -bX Or with: # cyclictest [...] -bX --tracemark Also, how do I reproduce your issue? Are you doing tracing by hand? More comments below.
quoted hunk ↗ jump to hunk
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 <redacted> --- 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); }
We do tracing(0) when we hit the latency threshold, so I don't think this is necessary. However, have you checked that writing to tracing_on won't break trace-cmd when it exec()ed cyclictest?
quoted hunk ↗ jump to hunk
@@ -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)