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.

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)