Date: Tue, 18 Mar 2014 14:26:19 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: freebsd-hackers@freebsd.org, soc-status@freebsd.org, yan cui <ccuiyyan@gmail.com> Subject: Re: FreeBSD GSOC proposal in 2014 Message-ID: <201403181426.19929.jhb@freebsd.org> In-Reply-To: <20140314070218.GA37327@FreeBSD.org> References: <CAAVq3rkyqmu6fKL9jFX6NmwaiB794H5fN_Ec79GYG39GHfh2Ow@mail.gmail.com> <CAAVq3rmQVZqvmF7bg0=9oHBrUDMegvmREKPe4E2RCfQ=3yxo9w@mail.gmail.com> <20140314070218.GA37327@FreeBSD.org>
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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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