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
> > 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?
> 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:
> Instead of porting witness to pthreads, maybe we could evaluate expanding
> WITNESS to cover kern_umtx? This could prove to be more universal.
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.
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