Re: FreeBSD GSOC proposal in 2014

Really? Maybe I can download his code from previous GSoC.
Actually, before applying for this idea, I did not scan the projects in
previous years and just pick up one which I like.
Are there any possibilities to improve on this part (or this idea should
not be considered any more)?

Yan


2014-03-18 14:26 GMT-04:00 John Baldwin <jhb_at_freebsd.org>:

> On Friday, March 14, 2014 3:02:18 am Wojciech A. Koszek wrote:
> > On Thu, Mar 13, 2014 at 09:56:35PM -0400, yan cui wrote:
> > > Hi all,
> > >
> > >     I write this mail to make my question clear. I know witness can be
> used
> > > to detect wrong lock order in the kernel. However, can it be used to do
> > > lock profiling (what I mean is to report the information such as which
> > > locks are most contended and print some related statistics such as
> calling
> > > graph, etc)?
> > > In other words, is it enough to finish the task by porting witness to
> the
> > > pthread library?
> > >
> >
> > Yan,
> >
> > To my knowledge WITNESS is the only tool for lock order verification.
> >
> > For lock profiling in the FreeBSD kernel there's a KTR subsystem. KTR
> > mechanism is basically like syslog() in the user-space, but for the
> kernel.
> > KTR subsystem will receive messages from KTR API that is placed in the
> > FreeBSD kernel. Messages get stored on the list of some sort. List can be
> > exported to a file. File you can later analyze.
> >
> > Jeff wrote a Python app which can be used for pre-processing the KTR logs
> > from scheduler and protting them visually. Link:
> >
> > http://svnweb.freebsd.org/base/head/tools/sched/schedgraph.py
> >
> > Instead of porting witness to pthreads, maybe we could evaluate expanding
> > WITNESS to cover kern_umtx? This could prove to be more universal.
> >
> > Wojciech
>
> There is a dedicated lock profiler (LOCK_PROFILING) in the kernel.  A
> previous GSoC student from an earlier year has already re-implemented both
> LOCK_PROFILING and WITNESS for pthreads.
>
> --
> John Baldwin
>



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