Re: Serious WAPL performance problems

[Mindaugas Rasiukevicius <rmind%netbsd.org@localhost>]

David Holland <dholland-tech%netbsd.org@localhost> wrote:
> On Tue, Oct 23, 2012 at 07:53:28PM +0200, Edgar Fu? wrote:
>  > > the output of ps -lax on the NFS server during the 18-20 second
>  > > window
>  >
>  > As far as I remember (you need the s option, too), the main nfsd
>  > thread is on select, one subthread on biowait or biolock and the
>  > others on tstile.
> 
> It would really be nice to know what those others are waiting behind.
> 
> paging rmind...
> 
> 
> Explanation to those following along at home: rmind has been claiming
> for years that there is no need to have real wchan names instead of
> "tstile", which just means "I'm waiting for something". He claims it's
> easy to diagnose problems without that information. So when one comes
> up it's time for him to prove it. :-)
> 

"Easy to diagnose problems"?  Plain false.  The lock naming you are talking
about would give no *more* information than "it is a vnode lock", and one
can guess already that it is most likely the case here (what a surprise!).
To diagnose the problem, one needs quite more information than your useless
lock naming would provide: for example, in almost any case, backtraces of
the LWPs are required to figure out what is going on.  Unless the case is
very obvious/simplistic, lock naming will not explain the deadlock without
the backtraces.  I have said this multiple times.  If you are unable to see
the difference between the statements, then I cannot help you.  Nor I am
interested in discussion with somebody who does not bother to listen.

-- 
Mindaugas