Re: FreeBSD GSOC proposal in 2014

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

> 
> 2014-03-13 19:19 GMT-04:00 yan cui <ccuiyyan_at_gmail.com>:
> 
> > Hi all,
> >
> >     I have downloaded the newest FreeBSD-release kernel and scanned some
> > codes.
> > Wonder to know whether the lock order verification and lock profiling tool
> > mentioned in
> > the GSoC idea list is witness? Are there any other tools that needs to
> > look at in the FreeBSD kernel?
> >
> > Thanks, Yan
> >
> >
> > 2014-03-09 15:46 GMT-04:00 yan cui <ccuiyyan_at_gmail.com>:
> >
> > Hi All,
> >>
> >>      I am a student in Columbia University (Yan Cui), and want to join
> >> the FreeBSD GSOC 2014. After scanned the idea list posted online, I think I
> >> am interested in
> >>  the idea titled "user space pthread mutex lock contention profiling and
> >> lock order verification tools". I have several year experiences in kernel
> >> and user locking and believe I can complete the task in time. Currently, I
> >> wonder to know, before submitting an application on GSOC home page, do I
> >> need to submit some documents in the community (to review?)
> >>
> >> Best Wishes!
> >> Yan
> >>
> >> --
> >> Think big; Dream impossible; Make it happen.
> >>
> >
> >
> >
> > --
> > Think big; Dream impossible; Make it happen.
> >
> 
> 
> 
> -- 
> Think big; Dream impossible; Make it happen.
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-- 
Wojciech A. Koszek
wkoszek_at_FreeBSD.czest.pl
http://FreeBSD.czest.pl/~wkoszek/