This is the mail archive of the systemtap@sourceware.org mailing list for the systemtap project.
Index Nav: | [Date Index] [Subject Index] [Author Index] [Thread Index] | |
---|---|---|
Message Nav: | [Date Prev] [Date Next] | [Thread Prev] [Thread Next] |
Other format: | [Raw text] |
On 08/29/2016 09:26 PM, David Smith wrote:
On 08/28/2016 08:29 AM, Avi Kivity wrote:On 08/26/2016 11:07 PM, David Smith wrote:On 08/26/2016 01:39 PM, Avi Kivity wrote:On 08/25/2016 08:37 PM, David Smith wrote:On 08/25/2016 11:21 AM, Avi Kivity wrote:Hi, Should I wait for ongoing improvement here, or shall I look elsewhere for my tracing needs? It would be a pity (for me) if I have to find another solution, because systemtap has all the expressiveness and integration I need. But it has a dramatic impact on my application runtime. I was able to extract some useful data with perf probe/perf record, but as soon as I need to qualify a probe point with runtime information, perf falls short.As Frank mentioned in a previous email, it might be possible for us to switch to using straight kprobes instead of syscall tracing to handle mmap tracing. In your use case of calling epoll_wait() lots of times per second, that might be a *big* win. I'll see what can be done to add that feature.Thanks a lot. I'll be happy to test patches.OK, since you asked... Here's a patch I'm testing that tries to do prefiltering when a syscall occurs, so we don't have to take that lock. Please rebuild with it, and let me know if it (a) works, and (b) has lower overhead in your situation.With an unloaded system, systemtap almost vanishes from the profile. This is on a 2s24c48t system, running epoll_pwait() and polling on user memory locations in a tight loop.... stuff deleted ... After looking into it, Josh was right in thinking I had the test backwards. Can you try the following patch (after reverting the last patch) and let us know what you find?
With the new patch, I get ERROR: probe overhead exceeded threshold ERROR: probe overhead exceeded threshold WARNING: Number of errors: 2, skipped probes: 0 WARNING: /home/avi/systemtap.f23/bin/staprun exited with status: 1 Pass 5: run failed. [man error::pass5] with -g --suppress-time-limits, I get the usual spinlock badness.
Index Nav: | [Date Index] [Subject Index] [Author Index] [Thread Index] | |
---|---|---|
Message Nav: | [Date Prev] [Date Next] | [Thread Prev] [Thread Next] |